Hard disk and file system errors can result from a variety of problems, such as hardware failures, power outages, poor system maintenance, viruses, and human error. When troubleshooting problems related to disks and file systems, refer to this chapter for information about troubleshooting tools, volume and disk error conditions, viruses, and stop messages. You can also use this chapter to obtain detailed descriptions of the master boot record (MBR), the GUID partition table (GPT), and the boot sectors.

For information on how to obtain the Windows XP Professional Resource Kit in its entirety, please see http://www.microsoft.com/mspress/books/6795.asp.

On This Page

Related Information
New in Troubleshooting Disks and File Systems
Maintenance and Troubleshooting Tools
Disk and Volume Status Descriptions
Viruses That Affect the MBR and Boot Sectors
Repairing Damaged MBRs and Boot Sectors in x86-Based Computers
Stop Messages for Disks and File Systems
Other Disk Problems
Disk Sectors Critical to Startup
Additional Resources

Related Information

• For more information about the file allocation table (FAT) and NTFS file systems, see Chapter 13, “Working with File Systems.”

• For more information about managing disks and volumes, see Chapter 12, “Organizing Disks.”

• For more information about the tools that Microsoft Windows XP Professional provides for troubleshooting, see Appendix C, “Tools for Troubleshooting.”

• For more information about how to troubleshoot, see Chapter 27, “Understanding Troubleshooting.”

New in Troubleshooting Disks and File Systems

Microsoft Windows XP Professional provides improved troubleshooting tools for disks and file systems. Table 28-1 summarizes the enhancements made from Microsoft Windows 2000 to Windows XP Professional.

Table 28-1 Enhancements Since Windows 2000

New Feature	Feature Description
Automated System Recovery (ASR)	Automated System Recovery (ASR) is a two-part recovery system that allows you to restore the operating system state by using files saved to tape media and hard disk configuration information saved to a floppy disk.
Disk Defragmenter has new capabilities, including a command-line option.	Windows XP Professional offers two choices for defragmenting disks: the Disk Defragmenter snap-in and a new command-line version of the tool (Defrag.exe). Both tools can defragment NTFS volumes that have cluster sizes larger than 4 KB and files smaller than 16 clusters. Both tools can also defragment the master file table (MFT) on NTFS volumes.
Troubleshoot disks and volumes at the command line by using DiskPart.	Use the new command-line tool DiskPart to troubleshoot disks and volumes at the command line as an alternative to using the Disk Management snap-in.
Create GUID partition table disks on 64-bit computers.	Windows XP Professional x64 Edition supports a new partition style called GUID partition table (GPT). GPT disks contain redundant partition tables for improved partition structure integrity.
Use the Fsutil.exe tool to determine whether a volume is marked as dirty.	The Fsutil.exe command-line tool offers many commands to manage file system behavior. For example, use the fsutil dirty command to determine whether a volume is dirty. If a volume is dirty, it has experienced file system errors and you must run Chkdsk on the volume to repair the problem. You can also use the fsutil dirty command to mark a volume as dirty.

If you are migrating from Microsoft Windows NT version 4.0, the enhancements in Table 28-2 apply in addition to those outlined in Table 28-1.

Table 28-2 Enhancements Since Windows NT 4.0

New Feature	Feature Description
Chkntfs.exe	Chkntfs.exe is a command-line tool to disable the automatic running (at restart) of Chkdsk on dirty volumes. You can also use Chkntfs to cancel a scheduled session of Chkdsk so that it does not run when the computer restarts.
New Chkdsk parameters	Chkdsk offers two new parameters, /c and /i, to reduce the length of time required to run Chkdsk on NTFS volumes.
Recovery Console	Recovery Console is a command-line startup environment that allows you to gain access to the hard disk for basic troubleshooting and system maintenance.
Dmdiag.exe	Dmdiag.exe is a command-line tool that displays the location and layout of dynamic disks and volumes. Dynamic disks were new in Windows 2000 and do not use the traditional partition layout that was used by disks in Windows NT 4.0 and earlier.

Maintenance and Troubleshooting Tools

Windows XP Professional provides many tools to maintain and troubleshoot disks and file systems. The tools described in this section are:

• Chkdsk

• Disk Defragmenter

• Recovery Console

• Automated System Recovery

• DiskProbe

• Dmdiag

For more information about troubleshooting problems with Windows XP Professional, see Appendix C, “Tools for Troubleshooting,” and Chapter 27, “Understanding Troubleshooting.”

Chkdsk

Chkdsk.exe is a command-line tool that verifies the logical integrity of a file system on a Windows XP Professional volume. If file system structures become damaged, Windows XP Professional automatically schedules Chkdsk to run the next time the computer is restarted. At any time, you can manually run Chkdsk at the command prompt or from Windows Explorer or My Computer. For more information about running the graphical version of Chkdsk, see “Running Chkdsk from My Computer or Windows Explorer” later in this chapter.

Volumes that have file system errors are known as dirty volumes. To indicate that a file system problem has occurred and that the volume is dirty, Windows XP Professional displays a message similar to the following when you attempt to open, delete, or rename a file or folder by using Microsoft Windows Explorer or the command prompt:

Note: Some of the lines in the following code have been displayed on multiple lines for better readability.

The file or directory filename is 
corrupt and unreadable.
Please run the Chkdsk  utility.

You might also see messages in the system log in the Event Viewer snap-in. Figure 28-1 illustrates a Chkdsk entry in the system log.

To determine whether a volume is dirty use the fsutil dirty query command or the chkntfs command.

For example, to determine whether volume C is dirty, type:

fsutil dirty query c:

–or–

chkntfs c:

Running Chkdsk to Repair File Systems

You can run Chkdsk in two modes:

• Chkdsk without parameters.

  When you run Chkdsk without parameters, it runs in read-only mode. In this mode, Chkdsk examines the disk and then reports whether it found any file system errors but does not repair the errors.

• Chkdsk with parameters.

  When you run Chkdsk with parameters, such as /f or /r, Chkdsk repairs errors related to file system structures.

Before running Chkdsk to repair a volume

Before running Chkdsk to repair a volume, you must do the following:

• Back up key data files, or make sure that you have a known good backup.

• Be prepared to let the Chkdsk process complete.

If you use the /f or /r parameter on a large volume (for example, 70 GB) or on a volume with a very large number of files (in the millions), Chkdsk can take a long time to complete. The volume is not available during this time because Chkdsk does not relinquish control until it is done. If a volume is being checked during the startup process, the computer is not available until the Chkdsk process is complete.

Chkdsk does not include parameters that let you cancel the Chkdsk process; however, when you run Chkdsk you can specify parameters that shorten the process. For more information about minimizing downtime during Chkdsk, see “Reducing the Time Required to Run Chkdsk on NTFS Volumes” later in this chapter.

Running Chkdsk on the boot volume

When you use the /f or /r parameters to run Chkdsk on the boot volume, Chkdsk displays the following message:

Note: Some of the lines in the following code have been displayed on multiple lines for better readability.

Chkdsk cannot run because the volume 
is in use by another process. Would 
you like to schedule this volume to 
be checked the next time the system 
restarts? (Y/N)

Chkdsk cannot gain exclusive use of the boot volume because it contains the Windows XP operating system files. Therefore, Chkdsk must always restart the computer to check the boot volume. If you press the Y key, a version of Chkdsk known as Autochk runs the next time the computer restarts. After Autochk checks the boot volume, the computer automatically restarts.

Running Chkdsk on a volume other than the boot volume

When you use the /f or /r parameters on a volume other than the boot volume, Chkdsk must lock the volume for exclusive use before it can repair errors. If the volume has open files or programs, Chkdsk displays the following message:

Note: Some of the lines in the following code have been displayed on multiple lines for better readability.

Chkdsk cannot run because the 
volume is in use by another process. 
Chkdsk may run if this volume is 
dismounted first. ALL OPEN HANDLES 
TO THIS VOLUME WOULD THEN BE  INVALID. 
Would you like to force 
a dismount on this volume? (Y/N)

If you press the Y key, Chkdsk attempts to close all handles and lock the volume. If Chkdsk is successful in locking the volume, the repair process begins. The duration of the repair process is determined by the number of files and folders on the volume and the level of damage, if any.

If Chkdsk cannot lock the volume, or if you press the N key, you can specify that you want to check the volume by running Autochk the next time the computer restarts. For more information about Autochk, see “Running Autochk When the Computer Restarts” later in this chapter.

Chkdsk Syntax

The command-line syntax for Chkdsk is as follows:

Note: Some of the lines in the following code have been displayed on multiple lines for better readability.

chkdsk [volume[[path] filename]]
[/f][/v][/r][/x][/i][/c][/l[:size]]

Chkdsk parameters

Table 28-3 lists all Chkdsk command-line parameters.

Table 28-3 Chkdsk Parameters

Parameter	Description
volume	Specifies the volume that you want Chkdsk to check. You can specify the volume by using any of the formats in the following examples: To run Chkdsk on the C volume, specify: c: To run Chkdsk on a mounted volume called data that is mounted on the C volume, specify: c:\data To run Chkdsk on a volume, specify the symbolic link name for a volume, such as: \\?\Volume{2d9bd2a8-5df8-11d2-bdaa-000000000000} You can determine a symbolic link name for a volume by using the mountvol command. For more information about mountvol, see Windows XP Professional Help.
path	FAT/FAT32 only. Specifies the location of a file or set of files within the folder structure of the volume.
filename	FAT/FAT32 only. Specifies the file or set of files to check for fragmentation. Wildcard characters (* and ?) are allowed.
/f	Fixes errors on the disk. The volume must be locked. If Chkdsk cannot lock the volume, Chkdsk offers to check it the next time the computer restarts.
/v	On FAT/FAT32: Displays the full path and name of every file on the disk. On NTFS: Displays additional information or cleanup messages, if any.
/r	Locates bad sectors and recovers readable information (implies /f). If Chkdsk cannot lock the volume, it offers to check it the next time the computer starts. Because NTFS also identifies and remaps bad sectors during the course of normal operations, it is usually not necessary to use the /r parameter unless you suspect that a disk has bad sectors.
/x	Forces the volume to dismount first, if necessary. All opened handles to the volume are then invalid (implies /f). This parameter does not work on the boot volume. You must restart the computer to dismount the boot volume.
/i	NTFS only. Performs a less detailed check of index entries, reducing the amount of time needed to run Chkdsk.
/c	NTFS only. Skips the checking of cycles within the folder structure, reducing the amount of time needed to run Chkdsk.
/l:size	NTFS only. Changes the size of the log file to the specified number of kilobytes. Displays the current size if you do not enter a new size. If the system loses power, stops responding, or is restarted unexpectedly, NTFS runs a recovery procedure when Windows XP Professional restarts that accesses information stored in this log file. The size of the log file depends on the size of the volume. In most conditions, you do not need to change the size of the log file. However, if the number of changes to the volume is so great that NTFS fills the log before all metadata is written to disk, NTFS must force the metadata to disk and free the log space. When this condition occurs, you might notice that Windows XP Professional stops responding for 5 or more seconds. To eliminate the performance impact of forcing the metadata to disk, increase the size of the log file. For more information about NTFS recoverability, see Chapter 13, “Working with File Systems.”
/?	Displays this list of Chkdsk parameters.

For more information about the Chkdsk parameters, see Windows XP Professional Help. For more information about running the graphical version of Chkdsk, see “Running Chkdsk from My Computer or Windows Explorer” later in this chapter.

Chkdsk examples

To run Chkdsk to repair errors on the D volume, type:

chkdsk d: /f

If you need to run Chkdsk on a large D volume and you want Chkdsk to complete as quickly as possible, type:

chkdsk d: /f /c /i

You can script Chkdsk and Autochk by using the Windows Management Instrumentation (WMI) classes Win32_LogicalDisk, Win32_AutoChkSetting, and Win32_OperatingSystemAutochkSetting. For more information about WMI, see the Microsoft Windows Management Instrumentation (WMI) SDK link on the Web Resources Page at http://www.microsoft.com/windows/reskits/webresources.

The Chkdsk Process on NTFS Volumes

When you run Chkdsk on NTFS volumes, the Chkdsk process consists of three major stages, and optional fourth and fifth stages. Chkdsk displays its progress for each stage with the following messages:

Note: Some of the lines in the following code have been displayed on multiple lines for better readability.

CHKDSK is verifying files (stage 1 of 3)... 
File verification completed. CHKDSK is verifying 
indexes (stage 2 of 3)... Index verification 
completed. CHKDSK is verifying security 
descriptors (stage 3 of 3)... Security descriptor 
verification completed.

The following describes each of the Chkdsk stages.

Stage 1: Chkdsk verifies each file record segment in the master file table

During stage 1, Chkdsk examines each file record segment in the volume’s master file table (MFT). A specific file record segment in the MFT uniquely identifies every file and directory on an NTFS volume. The percent complete that Chkdsk displays during this phase is the percent of the MFT that has been verified.

Stage 2: Chkdsk checks the directories in the volume

During stage 2, Chkdsk examines each of the indexes (directories) on the volume for internal consistency and verifies that every file and directory represented by a file record segment in the MFT is referenced by at least one directory. Chkdsk also confirms that every file or subdirectory referenced in each directory actually exists as a valid file record segment in the MFT, and it checks for circular directory references. Chkdsk then confirms that the time stamps and the file size information associated with files are up to date in the directory listings for those files.

The percent complete that Chkdsk displays during this phase is the percent of the total number of files on the volume that are checked. For volumes with many thousands of files and folders, the time required to complete this stage can be significant.

Stage 3: Chkdsk verifies the security descriptors for each volume

During stage 3, Chkdsk examines each of the security descriptors associated with each file and directory on the volume by verifying that each security descriptor structure is well formed and internally consistent. The percent complete that Chkdsk displays during this phase is the percent of the number of files and directories on the volume that are checked.

Stages 4 and 5 (optional stages): Chkdsk reads every sector on the volume to confirm stability

Chkdsk performs stages 4 and 5 if you specify the /r parameter when you run Chkdsk. The /r parameter confirms that the sectors in each cluster are usable. Specifying the /r parameter is usually not necessary because NTFS identifies and remaps bad sectors during the course of normal operations, but use the /r parameter if you suspect the disk has bad sectors.

During stage 4, Chkdsk verifies all clusters in use; during stage 5, Chkdsk verifies unused clusters.

The percent complete that Chkdsk displays during stage 4 is based on the percent of used clusters that are checked. The percent complete that Chkdsk displays during stage 5 is the percent of unused clusters that are checked. Used clusters typically take longer to check than unused clusters, so stage 4 lasts longer than stage 5 on a volume with equal amounts of used and unused clusters. For a volume with mostly unused clusters, stage 5 takes longer than stage 4.

During stages 1 and 3, the percent complete indicator advances relatively smoothly, although some unevenness might occur in the rate at which these phases progress. For example, file record segments that are not in use require less time to process than do those that are in use, and larger security descriptors take more time to process than do smaller ones. Overall, the percent complete is a fairly accurate representation of the actual time required for that phase.

The duration of stage 2 varies because the amount of time required to process a directory is closely tied to the number of files or subdirectories listed in that directory. Because of this dependency, the percent complete indicator might not advance smoothly during stage 2, though the indicator continues to advance even for large directories. Therefore, do not use the percent complete as a reliable representation of the actual time remaining for this phase.

For more information, see “Determining How Long Chkdsk Will Run” later in this chapter.

Running Autochk When the Computer Restarts

Autochk.exe is a version of Chkdsk that runs only before Windows XP Professional starts. Autochk runs in the following situations:

• Autochk runs if you try to run Chkdsk on the boot volume.

  Chkdsk cannot dismount the boot volume, so Chkdsk offers to run the repair process by using Autochk when the computer is restarted. If you press the Y key to schedule Autochk, you have 10 seconds after the computer restarts to press any key and cancel the repair process. If you cancel Autochk before the 10-second delay lapses, Autochk does not run the next time you restart the computer. If you want to run Chkdsk again, you can do so from the command line.

• Autochk runs if Chkdsk cannot gain exclusive use of the volume.

  If Chkdsk cannot gain exclusive use of a volume when you run Chkdsk from the command line, Chkdsk offers to dismount the volume. If you press the Y key and Chkdsk still cannot dismount the volume, or if you press the N key, Chkdsk offers to run the repair process by using Autochk when the computer is restarted. If you press the Y key to schedule Autochk, you have 10 seconds after the computer restarts to press any key and cancel the repair process. If you cancel Autochk before the 10-second delay lapses, Autochk does not run the next time you restart the computer. If you want to run Chkdsk again, you can do so from the command line.

• Autochk runs if the volume is flagged as dirty.

  If the file system has flagged the volume as dirty, Autochk runs the repair process at startup. Volumes are flagged as dirty when the file system detects an error on the volume. If Autochk detects a dirty volume, it provides a 10-second delay and then begins the repair process. If you cancel Autochk when a volume is dirty, Autochk attempts to run again after a 10-second delay each time the computer is restarted.

Use the Chkntfs.exe command-line tool to change the Autochk delay from 0 seconds to up to 3 days (259,200 seconds). However, a long delay means that the computer does not start until the time elapses or until you press a key to cancel Autochk.

If you choose to let Autochk run, you can review the Autochk report in the application log of the Event Viewer snap-in. Autochk information is logged by the Winlogon service, so look for entries with Winlogon listed as the source of the entry.

Note You can use the fsutil dirty command to query and set the volume as dirty, but you must use the chkntfs command to exclude a dirty volume from being repaired by Autochk. For more information about using the fsutil dirty command, see Windows XP Professional Help.

Using Chkntfs to Prevent Autochk from Running

For heavily used computers that cannot be offline for the length of time required to complete the repair process, use the Chkntfs.exe command-line tool to exclude dirty volumes from being checked by Autochk. You can also use Chkntfs to cancel previously scheduled sessions of Autochk and to check the status of a volume.

For example, type chkntfs c: at the command prompt to determine:

• Whether you manually scheduled Autochk to run on volume C at the next reboot.

• Whether volume C is dirty, in which case Autochk runs automatically the next time the computer is restarted unless you manually run Chkdsk on volume C, cancel Autochk during the delay at startup, or exclude volume C by using the /x parameter.

  Caution If a volume is flagged as dirty, do not postpone running Chkdsk indefinitely. File  system damage can become worse over time, so you must consider dirty volumes at risk until you run Chkdsk. Use Chkntfs only if you need to control when Chkdsk is run.

Chkntfs syntax

The command-line syntax for Chkntfs is as follows:

chkntfs volume [...] 
chkntfs [/d] 
chkntfs [/t[:time]] 
chkntfs [/x volume [...]] 
chkntfs [/c volume [...]]

Chkntfs parameters

Table 28-4 lists all Chkntfs command-line parameters. When using Chkntfs, you can specify only one parameter at a time.

For more information about the Chkntfs parameters, see Windows XP Professional Help. For more information about the registry changes that occur when you use Chkntfs, see article 218461, “Description of Enhanced Chkdsk, Autochk, and Chkntfs Tools in Windows 2000.” To find this article, see the Microsoft Knowledge Base link on the Web Resources page at http://www.microsoft.com/windows/reskits/webresources.

Table 28-4 Chkntfs Parameters

Parameter	Description
volume [...]	Specifies the volume that you want to check. Specify the volume using one of the following formats: To run Chkntfs on the C volume, specify: c: To run Chkdsk on a mounted volume called data that is mounted on the C volume, specify: c:\data To run Chkntfs on a volume, you can specify the symbolic link name for a volume, such as: \\?\Volume{2d9bd2a8-5df8-11d2-bdaa-000000000000} You can determine a symbolic link name for a volume by using the mountvol command. For more information about mountvol, see Windows XP Professional Help.
[/d]	Restores all Chkntfs default settings except the countdown time for Autochk. The /d parameter clears the list of volumes you excluded with the /x parameter, and it also cancels any sessions of Autochk previously scheduled to take place when the computer restarts. After you use the /d parameter, Autochk runs on volumes that are flagged as dirty when the computer restarts.
[/t[:time]]	Changes the Autochk initiation countdown time to the specified amount of time entered in seconds. The default countdown time is 10 seconds. If you use the /t parameter without using :time, the countdown time that you last used is displayed.
[/x volume [...]]	Excludes the specified volume from being checked when the computer starts. This parameter excludes only dirty volumes; Autochk still checks the volumes that you manually schedule.
[/c volume [...]]	Schedules Autochk to run on the specified volumes if they are dirty when the computer starts, overriding any volumes excluded by the /x parameter.

Using the /x parameter to exclude volumes

Use the /x parameter to prevent Autochk from running on known dirty volumes. Use this parameter only as a temporary measure. For example, when you know the volume is dirty, use the /x parameter to postpone running Autochk until a period of low computer activity, such as nights or weekends.

The /x parameter is not cumulative. Each time you use the /x parameter, you override the previous entry. For example, typing chkntfs e: /x, followed by chkntfs f: /x, excludes only the F volume from being checked.

To exclude multiple volumes, list them all in one command. For example, to exclude both the E and F volumes, type:

chkntfs e: f: /x

Using the /c parameter to run Autochk on excluded volumes

If you use Chkntfs to determine that an excluded volume is marked as dirty and if you want Autochk to run on the volume when the computer starts, use the /c parameter. The /c parameter overrides the /x parameter so that you can run Autochk on volumes that you previously excluded. After Autochk runs on the volume, the volume remains on the excluded list.

Note Use the chkdsk /f or chkdsk /r command to check volumes that you previously excluded by using the chkntfs /x command. The chkntfs /c command runs Autochk only at startup and only if the volume is marked as dirty.

The /c parameter is cumulative. For example, specify multiple volumes by typing:

chkntfs c: /c chkntfs d: /c chkntfs e: /c

You can specify multiple volumes at the same time by typing:

chkntfs c: d: e: /c

Tip For more information on how to prevent Chkdsk and Autochk from running when you shut down or restart your computer, see article 831426, “Chkdsk.exe or Autochk.exe starts when you try to shut down or restart your computer,” in the Microsoft Knowledge Base.

Reducing the Time Required to Run Chkdsk on NTFS Volumes

NTFS is a journaling file system because it guarantees the consistency of the volume by using standard transaction logging and recovery techniques. If a disk becomes corrupted, NTFS runs a recovery procedure that accesses information stored in a transaction log file. The NTFS recovery procedure guarantees that the volume is restored to a consistent state. For this reason, it is unlikely that NTFS volumes might become corrupted.

Caution NTFS does not guarantee the integrity of user data following an instance of disk corruption, even when a full Chkdsk is run immediately after corruption is detected. Chkdsk might not recover all files, and files that are recovered might be internally corrupted. Therefore, you must protect important data by performing periodic backups.

If file system errors do occur on an NTFS volume, you must run Chkdsk to repair the damage. The recommended procedure is to run chkdsk /f as soon as possible, but you can also run a shorter version of Chkdsk by using the /c and /i parameters. These parameters were designed for administrators who manage exceptionally large NTFS volumes and who require flexibility in managing the downtime that is incurred when Chkdsk is running.

Caution Using the /c and /i parameters can result in a volume remaining corrupted after Chkdsk completes. Therefore, you must use these parameters only in situations where you need to keep system downtime to a minimum.

Table 28-5 provides a brief overview of each parameter and the potential reduction in Chkdsk duration. The actual reduction depends on a combination of factors, such as the ratio of files to directories and the relative speed of disk input/output (I/O) versus CPU speed, making the completion time difficult to predict.

Table 28-5 Overview of the /c and /i Chkdsk Parameters

Parameter	What It Does	Potential Reduction in Chkdsk Duration
/c	Skips the process that detects cycles in the directory structure.	1 to 2 percent
/i	Skips the process that compares directory entries to the file record segments that correspond to those entries.	50 to 70 percent

Using the /c parameter

Use the /c parameter to skip the process that detects cycles in the directory structure. Cycles are a rare form of corruption in which a subdirectory has itself as a parent. Although you can speed up the Chkdsk process by using the /c parameter, using the /c parameter can also leave directory loops on an NTFS volume. Such loops might be inaccessible from the rest of the directory tree and could result in orphaned files. Files can become orphaned when file record segments remain but are not referenced by any directory entry. The file represented by the file record segment might be intact in all ways except that the file is invisible to all programs, including backup programs.

Using the /i parameter

Use the /i parameter to skip the process that compares directory entries to the file record segments that correspond to those entries. A file record segment in the master file table (MFT) uniquely identifies every file and directory in an NTFS volume. When you use the /i parameter, the directory entries are checked to verify that they are self-consistent, but the directory entries are not necessarily consistent with the data stored in their corresponding file record segments.

When you use the /i parameter, files can become orphaned if directory entries remain but the directory entries refer to incorrect file record segments. In this case, the files exist, but programs encounter errors when attempting to access them.

For more information about using the /i and /c parameters, see article 187941, “An Explanation of CHKDSK and the New /C and /I Switches.” To find this article, see the Microsoft Knowledge Base link on the Web Resource page at http://www.microsoft.com/windows/reskits/webresources.

Running Chkdsk on Mission-Critical Computers

If you use the Chkntfs or Fsutil command-line tool and discover that a volume in a mission-critical computer is flagged as dirty, you must choose among the following three choices:

Do nothing.

For a mission-critical computer that is expected to be online 24 hours a day, doing nothing might be a necessary choice. The drawback to this option is that relatively minor corruption can become major corruption if you do not repair the volume as soon as possible after you detect the corruption. Therefore, consider this option only if keeping a system online is more important than the integrity of the data stored on the corrupted volume. You must consider all data on the corrupted volume at risk until you run Chkdsk.

Run a full Chkdsk.

This option repairs all file system data, restoring all user data that can be recovered by means of an automated process. The drawback is that a full Chkdsk might require several hours of downtime for a mission-critical computer at an inopportune time.

Run an abbreviated Chkdsk by using a combination of the /c and /i parameters.

This option repairs minor corruption that can become major corruption in much less time than a full Chkdsk requires, but it might not repair all corruption. A full Chkdsk is required to guarantee that all the data that can be recovered has been recovered.

Determining How Long Chkdsk Will Run

The best way to predict how long Chkdsk will take to run on a given volume is to perform a trial run in read-only mode during a period of low system usage. However, you must use caution when using read-only mode to estimate run time because of the following reasons:

Chkdsk might fail in read-only mode or might report false errors.

The read-only Chkdsk process involves three phases. If Chkdsk encounters errors in the early phases, Chkdsk might abort before it completes all three phases. In addition, Chkdsk is prone to falsely reporting errors when in read-only mode, and it might report that a volume is corrupted even when no corruption is present. For example, Chkdsk might report corruption if NTFS modifies an area of the disk on behalf of a program at the same time Chkdsk is examining the same area. To verify a volume correctly, the volume must be in a static state, and the only way to guarantee that state is to lock the volume. Chkdsk locks the volume only when you specify the /f, /r, or /x parameters. Thus, you might need to run Chkdsk more than once for Chkdsk to complete all stages in read-only mode.

System load can influence the time required to run Chkdsk.

Chkdsk is both CPU intensive and disk intensive. If heavy disk I/O or high CPU usage is occurring when you run Chkdsk in read-only mode, the time required to complete the process increases.

Chkdsk and Autochk do not take the same time to complete.

Chkdsk runs while Windows XP Professional is running, and Autochk runs before Windows XP Professional loads. Although running Autochk at startup gives exclusive use of CPU and disk I/O resources to Chkdsk, it also deprives Autochk of the benefit of virtual memory. Thus, while Autochk usually runs faster than Chkdsk, systems with relatively low amounts of RAM might see longer times for Autochk than for Chkdsk.

Repairing corruption lengthens the Chkdsk process.

The read-only Chkdsk process can complete only if no significant corruption is found. If a disk suffers only minor corruption, the time to fix the problems is only slightly longer than the time required for read-only Chkdsk. However, if the volume has major corruption, the time required to run Chkdsk can increase in proportion to the number of files damaged.

Recovering Lost Clusters on FAT Volumes

Because some repairs on FAT volumes, such as correcting lost clusters (also known as allocation units) or cross-linked files, change the volume’s file allocation table and can cause data loss, Chkdsk first prompts you with a confirmation message similar to the following:

10 lost allocation units found in 3 chains.
Convert lost chains to files? (Y/N)

If you press the N key, Windows XP Professional fixes the errors on the volume but does not save the contents of the lost clusters.

If you press the Y key, Windows XP Professional attempts to identify the folder to which they belong. If the folder is identified, the lost cluster chains are saved as files.

If Windows XP Professional cannot identify the folder or if the folder does not exist, it saves each chain of lost clusters in a folder called Found.xxx, where xxx is a sequential number starting with 000. If no folder Found.000 exists, one is created at the root. If one or more sequential folders called Found.xxx (starting at 000) exist, a folder that uses the next number in the sequence is created.

Windows XP Professional creates Found.xxx folders as hidden system folders. To see a list of Found.xxx folders, at the root folder in the command prompt, type dir /a. For information about viewing hidden system folders in My Computer or Windows Explorer, see Windows XP Professional Help.

After the storage folder has been identified or created, one or more files with a name in the format Filennnn.chk are saved. (The first saved file is named File0000.chk, the second is named File0001.chk, and so on in sequence.) When Chkdsk finishes, you can examine the contents of these files with a text editor such as Notepad to see whether they contain any needed data (if the converted chains came from corrupted binary files, they are of no value). You can delete the .chk files after you save any useful data.

Caution Because other programs might create and use files with the .chk extension, you must be careful to delete only the .chk files that are in the Found.xxx folders.

Running Chkdsk from My Computer or Windows Explorer

In addition to using the command-line version of Chkdsk, you can run Chkdsk from My Computer or Windows Explorer. The graphical version of Chkdsk offers the equivalent of read-only mode, the /f parameter, and the /r parameter.

If Chkdsk cannot lock the volume, you can schedule Autochk to run the next time you restart the computer. You cannot choose to dismount the volume like you can when you use the command-line version of Chkdsk, nor can you use other Chkdsk parameters, such as /c or /i. To take advantage of all the Chkdsk parameters, use the command-line version of Chkdsk.

To run Chkdsk from My Computer or Windows Explorer

1. In My Computer or Windows Explorer, right-click the volume you want to check, and then click Properties.

2. On the Tools tab, click Check Now.

3. Do one of the following:

   • To run Chkdsk in read-only mode, click Start.

   • To run Chkdsk by using the /f parameter, select the Automatically fix file system errors check box and then click Start.

   • To run Chkdsk by using the /r parameter, select the Scan for and attempt recovery of bad sectors check box and then click Start.

Disk Defragmenter

Fragmentation causes your disk subsystem to perform more seeks, which slows the transfer rate and results in sluggish disk performance. Defragmenting is occasionally necessary because of the way files are stored on disk. Fragmentation can occur when:

• You create a file, but the volume does not have a group of contiguous, free clusters that is large enough to contain the entire file. Therefore, the file is broken into fragments rather than residing in contiguous clusters on the disk.

• You edit a file so that it outgrows its existing space on the disk. When a file uses all the clusters in a group of contiguous, free clusters, the file is then broken into fragments that are stored in free clusters elsewhere on the disk.

Although FAT and NTFS are designed to make storage faster and more efficient when you save files, these file systems take longer to read and write fragmented files than unfragmented files. When the files on a disk become badly fragmented, performance noticeably suffers because the disk heads must move to different tracks on the disk to locate all the clusters of the file.

Defragmentation tools fix this problem by moving the files into contiguous clusters on the disk. Reducing fragmentation reduces the amount of mechanical movement required to locate all clusters of a file, which improves hard disk performance.

Windows XP Professional provides two methods for defragmenting FAT and NTFS volumes:

• The Disk Defragmenter snap-in (Dfrg.msc).

• The new Disk Defragmenter command-line tool (Defrag.exe).

Both tools rearrange files, folders, programs, and unused space on your computer’s hard disk to optimize disk performance. In addition, the defragmentation tools are improved in Windows XP Professional so that you can:

• Defragment volumes that use any cluster size.

• Defragment files that are smaller than 16 clusters.

• Defragment the master file table (MFT).

The amount of time that the defragmentation process takes depends on several factors, including the size of the volume, the number and size of files on the volume, the amount of fragmentation, and how busy the system is during defragmentation.

Before Using the Disk Defragmentation Tools

When you use the disk defragmentation tools, keep the following restrictions in mind:

• You can defragment only local volumes, and you can defragment only one volume at a time.

• You must be logged on as an administrator or as a member of the Administrators group to defragment volumes.

• You cannot use the Disk Defragmenter command-line tool (Defrag.exe) while the Disk Defragmenter snap-in is open.

• You cannot defragment volumes that are marked as dirty by the file system. You must run Chkdsk on the dirty volume before you can defragment it. To determine whether a volume is dirty, use the fsutil dirty query command. For more information about running Chkdsk, see “Chkdsk” earlier in this chapter.

In addition, to obtain best results when you use the disk defragmentation tools, follow these guidelines:

• Ensure you have at least 15 percent free disk space when you defragment a volume. Windows XP Professional uses the free disk space as a sorting area for file fragments.

  Although the defragmentation tools can partially defragment volumes that have less than 15 percent free space, for best results delete unneeded files or move them to another volume to increase the free space to at least 15 percent. You can also use the Disk Cleanup tool to delete unnecessary files. For more information about Disk Cleanup, see Windows XP Professional Help.

• Do not run Backup (either a manual or a scheduled start) at the same time that you run the defragmentation tools because using Backup causes the defragmentation process to pause.

  The Backup program included with Windows XP Professional uses volume snapshots to allow users or applications to continue working while a backup occurs. The defragmentation process resumes after Backup removes the volume snapshot. For more information about volume snapshots, see Chapter 14, “Backing Up and Restoring Data.”

Running the Disk Defragmenter Snap-in

By using the Disk Defragmenter snap-in, you can analyze the volume before you defragment to see how many fragmented files and folders exist. If 10 percent or more of the files and folders are fragmented, Disk Defragmenter recommends that you defragment the volume. If the volume is less than 10 percent fragmented, you can still defragment the volume or you can simply view the fragmentation report.

To open the Disk Defragmenter snap-in

• Click Start, click Run, type dfrg.msc, and then click OK.

Figure 28-2 shows that the Disk Defragmenter snap-in is divided into two main areas. The upper part lists the volumes on the local computer and allows you to select a volume to analyze and defragment. The lower part displays a graphical representation of how fragmented the volume is. The colors indicate the condition of the volume:

• Red areas show fragmented files.

• Blue areas show contiguous (unfragmented) files.

• White areas show free space on the volume. White areas on an NTFS volume might also represent the MFT zone. For more information about the MFT zone, see Chapter 13, “Working with File Systems.”

• Green areas show files that cannot be moved. The green areas usually represent the paging file, but on NTFS volumes, green areas might also represent space used by the NTFS change journal and the NTFS log file.

By comparing the Estimated disk usage before defragmentation band to the Estimated disk usage after defragmentation band, you can see the improvement in your volume after defragmenting. The defragmentation report provides further details on the fragmentation state of the volume. Analyze volumes regularly and defragment them when Disk Defragmenter recommends it.

Defragmenting Volumes by Using the Defrag Command

The Disk Defragmenter command-line tool and the Disk Defragmenter snap-in both defragment volumes by using the same method. However, the command-line tool differs from the snap-in in the following ways:

• The command does not provide a graphical analysis of a volume’s fragmentation status, but it does provide a summary.

• The command does not provide a status indicator.

To see a list of parameters for Defrag.exe, at the command prompt, type:

defrag /?

To defragment a volume, specify the drive letter. For example, to defragment the C volume, type:

defrag c:

To defragment the C volume and view a detailed report that is similar to the report shown in the Disk Management snap-in, type:

defrag c -v

To analyze the C volume and view a detailed analysis report, type:

defrag c: -a -v

While the command-line Disk Defragmenter is analyzing and defragmenting a volume, it displays a blinking cursor. When Disk Defragmenter finishes analyzing a volume, it displays the analysis report. When Disk Defragmenter finishes defragmenting a volume, it displays the defragmentation report. After the process completes, Disk Defragmenter exits to the command prompt.

To interrupt the defragmentation process, at the command line, press Ctrl+C.

For more information about using Defrag.exe, see Windows XP Professional Help.

Tips for Using the Disk Defragmentation Tools

For best results when defragmenting volumes, follow these tips:

• Before defragmenting a volume, delete any unnecessary files, such as temporary files. You can delete unnecessary files by using Disk Cleanup. For more information about Disk Cleanup, see Windows XP Professional Help.

• Defragment a volume before you add a large number of files to the volume, such as before you install programs. This ensures that the files occupy contiguous space and do not become fragmented after you add them.

• Defragment a volume after you delete a large number of files from the volume.

• Defragment a volume after you install programs on it.

• Defragment the system and boot volumes after installing Windows XP Professional.

• Defragment volumes during periods of low system activity.

Optimizing Startup Times by Using Defragmentation Tools

Windows XP Professional monitors the files that are used when the computer starts and when you start applications. By monitoring these files, Windows XP Professional can prefetch them. Prefetching data is the process whereby data that is expected to be requested is read ahead into the cache. Prefetching boot files and applications decreases the time needed to start Windows XP Professional and start applications.

Prefetching is further improved if the files are located next to each other on the outer edge of the disk. Windows XP Professional optimizes the location of boot files and applications when the computer is idle. The optimization occurs in the background and lasts only a minute or two; you might hear the hard disk being accessed when optimization occurs. After the initial optimization takes place, subsequent optimization occurs, at most, every three days.

When you run the Disk Defragmenter tools that are included with Windows XP Professional, they can perform any optimization updates that are scheduled to take place during the next idle period. The Disk Defragmenter tools do not disturb the existing layout of optimized boot files and applications.

Note Computers running Windows XP Home Edition also prefetch and optimize boot files and applications.

Files That You Cannot Defragment

After you defragment a volume, you can view the defragmentation report to see the results. The report includes a list of files that remain fragmented (having two or more fragments). Some reasons that a file might remain fragmented include:

• The volume lacks adequate contiguous free space to defragment all files. Disk Defragmenter requires at least 15 percent free disk space to completely defragment a volume.

• During defragmentation, a new file is created on the volume in disk space that was previously free space. In this case, if Disk Defragmenter tries to move a file to that space to defragment the file, the move fails and the file remains fragmented.

• The file is the master file table (MFT) on an NTFS volume. Because the first fragment of the MFT cannot be moved, the MFT is typically contained within two fragments when sufficient space is available on the volume. If the MFT is contained within three or more fragments, Disk Defragmenter looks for free space where the MFT might fit. If sufficient free space exists, the MFT is moved as a whole (minus the first fragment). If space is not available, the MFT is not defragmented.

• The file is permanently excluded, in which case it might appear in the defragmentation report as still being fragmented no matter how many times you defragment the volume. The following files are permanently excluded from being defragmented.

  • Bootsect.dos

  • Safeboot.fs

  • Safeboot.csv

  • Safeboot.rsv

  • Hiberfil.sys

  • Memory.dmp

  • Paging file

The paging file is a hidden file on the hard disk that Windows XP Professional uses to hold parts of programs and data files that do not fit in memory. (The paging file and physical memory make up virtual memory.) In Windows 2000, the size of the paging file was conservative and often needed to be increased, which caused the paging file to become fragmented. Because Windows XP Professional creates a larger paging file than the default size used in Windows 2000, it is unlikely that your paging file will become fragmented.

You can determine whether the paging file is fragmented by analyzing the volume that contains the paging file and then viewing the analysis report. The report shows the size of the paging file and the number of fragments. You cannot use Disk Defragmenter to defragment the paging file because Windows XP Professional holds the paging file open for exclusive use. However, you can reduce the degree of fragmentation by deleting and then re-creating the paging file. You must have at least two volumes to perform this procedure.

To defragment the paging file

1. From the Start menu, click Control Panel, click Performance and Maintenance, and then click System.

2. On the Advanced tab, under Performance, click Settings.

3. On the Advanced tab, click Change to open the Virtual Memory dialog box.

4. In the list of drives, select a volume to store a temporary paging file.

5. Click Custom size, type an initial and maximum size to match the current paging file, and then click Set.

6. Select the original paging file in the drive list, reduce the minimum and maximum size of the original paging file to 0 MB, and then click Set.

7. Restart your computer to have the system use the new paging file.

8. Run Disk Defragmenter on the original volume to consolidate the free space segments created by moving the paging file.

9. Re-create the paging file on the original volume.

10. Reduce the minimum and maximum size of the temporary paging file to 0 MB.

11. Restart your computer.

Recovery Console

The Recovery Console is a text-mode command-line interpreter that you can use for basic troubleshooting and system maintenance. You can run the Recovery Console directly from the Windows XP operating system CD, or for x86-based systems install it as a startup option. The Recovery Console is separate from the Windows XP Professional command prompt and grants limited local hard disk access for both NTFS and FAT volumes.

Because starting the Windows XP Professional graphical user interface (GUI) is not a prerequisite for using the Recovery Console, Recovery Console can help you recover a Windows XP Professional-based computer that cannot start in safe mode or normal mode. For example, if the computer does not start because the master boot record (MBR) or boot sector is corrupted, you can use the Recovery Console to repair the MBR or boot sector.

Note Certain Recovery Console commands are not fully functional on dynamic disks or GPT disks.

For more information about using the Recovery Console to repair MBR and boot sector errors, see “Repairing Damaged MBRs and Boot Sectors in x86-Based Computers” later in this chapter.

For more information about installing and using Recovery Console, see Appendix C, “Tools for Troubleshooting.”

Automated System Recovery

If changes to the operating system cause instability or startup problems, you can use the Automated System Recovery (ASR) tool to restore the system state and all files stored on the system volume. The term system state refers to all the components that determine the current state of the operating system, including:

• User account information, hard disk configuration, and registry information that includes application, hardware, network, video, and software settings.

• Operating system files that are required to start the system, including those in the systemroot directory and boot files such as Ntldr or IA64ldr.efi.

ASR is a last resort option to use after you have unsuccessfully tried other recovery methods, such as rolling back drivers, restoring from backups, performing parallel installations, and using System Restore. ASR restores system state files and settings, and it restores your ability to start your system. For example, hard disk corruption might prevent you from starting Windows XP Professional, and the damage might be serious enough to prevent you from using safe mode, Recovery Console, or the Last Known Good Configuration. ASR automates the process of backing up and restoring system state information and files that are needed on the system volume to start Windows XP Professional.

ASR is accessible through the Windows XP Professional Backup application NTBackup.exe and through other programs created by independent software vendors (ISVs). ASR replaces the Emergency Repair Disk option found in Windows 2000 and Windows NT 4.0. For more information about using ASR and other recovery tools, see Chapter 14, “Backing Up and Restoring Data.”

DiskProbe

DiskProbe is a sector editor tool for Windows XP Professional that allows users who are members of the Administrators group to directly edit, save, and copy data on a physical hard disk. With careful use of DiskProbe, you can replace the master boot record (MBR), repair damaged partition table information, and repair or replace damaged boot sectors or other file system data. You can also use DiskProbe to save MBRs and boot sectors as backup binary files in case the original sectors become damaged by viruses, human error, hardware problems, power outages, or similar events. Unless you are familiar with using DiskProbe, try other troubleshooting tools, such as Recovery Console, before using DiskProbe.

Caution Be cautious when making any changes to the structures of your hard disk. Because DiskProbe does not validate the proposed changes to records, incorrect values in key data structures can render the hard disk inaccessible or prevent the operating system from starting. If you cannot correct the changes you entered, you must re-create and reformat all volumes on the disk.

DiskProbe can change the values of individual bytes in any sector on a dynamic disk, but it cannot navigate the structure of a dynamic disk. Therefore, use DiskProbe only on basic disks. You can, however, use DiskProbe to back up and restore the boot sector and MBR of dynamic disks.

DiskProbe is part of Windows Support Tools and is installed when the Complete check box is selected during setup. However, the Help for this tool contains the Windows 2000 version and is not included in Suptools.chm. The help for DiskProbe can be launched from the command line by typing dskprobe.hlp.

Caution Do not use DiskProbe on GPT disks in 64-bit computers. Structures on GPT disks are self-repairing. Making direct changes to GPT structures could cause the partition table checksums to become invalid, rendering the disk inaccessible. For more information about GPT disks, see “Disk Sectors on GPT Disks” later in this chapter.

Dmdiag

Dmdiag.exe is a command-line tool that displays the location and layout of dynamic disks (MBR and GPT) and dynamic volumes. This information is primarily useful if you are working with Microsoft Product Support Services to troubleshoot problems with dynamic disks and volumes.

Dmdiag.exe is part of Windows Support Tools and can be run from the command line by using the following syntax:

dmdiag [-f filename][-v][/?]

When used without parameters, Dmdiag.exe displays information about the dynamic disks and volumes installed on the computer. Table 28-6 describes the Dmdiag.exe parameters.

Table 28-6 Dmdiag.exe Parameters

Parameter	Description
-f filename	Specifies the name of the file that stores the output. If you do not specify an output file, the file is saved as Dmdiag.txt in the same folder where you run Dmdiag.exe. If you do not specify the -f parameter, the output is displayed at the command prompt.
-v	Runs Dmdiag in verbose mode, which contains additional information about dynamic disks and volumes. Use this mode to obtain a report that product support can use to help you troubleshoot dynamic disks and volumes.
/?	Displays a Help screen with usage syntax.

For more information about Dmdiag.exe, click Tools in Help and Support Center and then click Windows Support Tools.

Disk and Volume Status Descriptions

Members of the Administrators group can use the Disk Management snap-in to view the status of disks and volumes.

To open Disk Management

1. From the Start menu, click Run.

2. In the Open box, type diskmgmt.msc and then click OK.

As Figure 28-3 shows, if no errors are present on the disk, Disk Management displays an Online status for disks and a Healthy status for volumes.

You can use the information in this section to diagnose and resolve problems identified by Disk Management, which uses a number of predefined status descriptions to indicate a problem has occurred. In many cases, a problem with the underlying disk also results in a volume error condition. For example, Figure 28-4 shows a disk with the Online (Errors) error condition and a volume with the Healthy (At Risk) error condition.

You can also use the DiskPart command-line tool to view the status of disks and volumes. DiskPart is a text-mode command interpreter that is separate from the Windows XP Professional command prompt. DiskPart allows you to manage fixed (nonremovable) disks and volumes by using scripts or direct input.

To run DiskPart, at the command prompt, type:

diskpart

To view the status of disks, at the DiskPart command prompt, type:

list disk

To view the status of volumes, at the DiskPart command prompt, type:

list volume

To view a list of DiskPart commands, at the DiskPart command prompt, type:

commands

For more information about using DiskPart, see Windows XP Professional Help.

Disk Status Descriptions

The following status descriptions appear if Disk Management detects a problem with a disk or if Disk Management does not recognize the disk.

Foreign

The Foreign status occurs when you install a dynamic disk in the local computer. You must right-click the disk and then click Import Foreign Disks before you can access data on the disk. If you do not want to import the disk, you can right-click the disk and click Convert to Basic Disk. Disk Management displays a warning message before erasing all data from the disk and converting the disk to basic. For more information about importing foreign disks, see Chapter 12, “Organizing Disks.”

Missing

The Missing status occurs when a dynamic disk is corrupted, turned off, or disconnected. After you reconnect or turn on the missing disk, open Disk Management, right-click the missing disk, and then click Reactivate Disk.

Not Initialized

The Not Initialized status indicates that the disk does not contain a valid disk signature in the master boot record (MBR) or a valid disk GUID in the GUID partition table. After you install a new disk, Windows XP Professional must write the MBR or GUID partition table before you can create partitions on the disk.

When you first start Disk Management after installing a new disk, a wizard appears that provides a list of the new disks that Windows XP Professional detects. If you cancel the wizard before the MBR or GUID partition table is written, the disk status remains Not Initialized until you right-click the disk and then click Initialize Disk.

Offline

The Offline status occurs when a dynamic disk is not accessible. The disk might be corrupted or intermittently unavailable. Offline also appears if you attempt to import a foreign (dynamic) disk, but the import fails. An error icon appears on the offline disk. Only dynamic disks display the Offline status.

If the disk status is Offline and the disk name changes to Missing, the disk was recently available on the system but can no longer be located or identified. The missing disk might be damaged, turned off, or disconnected.

To bring a disk that is Offline and Missing back online

1. Repair any disk, controller, or cable problems and make sure that the physical disk is turned on, plugged in, and attached to the computer.

2. In Disk Management, right-click the disk, and then click Reactivate Disk to bring the disk back online.

If the disk status remains Offline and the disk name remains Missing, and you determine that the disk has a problem that cannot be repaired, you can remove the disk from the computer.

After you remove a dynamic disk from a computer, the remaining online dynamic disks retain information about the removed disk and its volumes in the dynamic disk database. You can delete all references to the removed disk by updating the dynamic disk database. To do this, use Disk Management to remove all volumes on the missing disk. After you remove all the volumes, right-click the missing disk and then click Remove Disk. The missing disk no longer appears in Disk Management.

Caution Deleting a volume destroys the data on the volume, so you should remove a disk only if you are absolutely certain that the disk is permanently damaged and unusable.

To bring a disk that is Offline but not Missing back online

1. In Disk Management, use the Reactivate Disk command to bring the disk back online.

2. If the disk status remains Offline, check the cables and disk controller and make sure that the physical disk is healthy. Correct any problems, and try to reactivate the disk again.

If the disk reactivation succeeds, any volumes on the disk automatically return to the Healthy status.

Online (Errors)

The Online (Errors) status indicates that I/O errors have been detected on a region of the disk. A warning icon appears on the disk with errors. Only dynamic disks display the Online (Errors) status.

If the I/O errors are transient, reactivate the disk by right-clicking the disk and then clicking Reactivate Disk to return the disk to the Online status.

Unreadable

The Unreadable status occurs when the disk is not accessible for the following reasons:

• The disk is spinning up.

• The disk might have experienced hardware failure, corruption, or I/O errors.

• The disk’s copy of the dynamic disk database might be corrupted.

An error icon appears on disks that display the Unreadable status. Both dynamic and basic disks display the Unreadable status.

Disks might display the Unreadable status while they are spinning up or when Disk Management is rescanning all the disks on the system. In some cases, an unreadable disk has failed and is not recoverable. For dynamic disks, the Unreadable status usually results from corruption or I/O errors on part of the disk, rather than failure of the entire disk. You can rescan the disks (by using the Rescan Disks command on the Action menu in Disk Management) or restart the computer to see whether the disk status changes.

Volume Status Descriptions

The following status descriptions appear if Disk Management detects a problem with dynamic volumes or if Disk Management does not recognize volumes, such as those created by non-Windows-brand operating systems.

Failed

The Failed status occurs when the dynamic disk is damaged or the file system is corrupted. Unless you can repair the disk or file system, the Failed status might indicate data loss.

To troubleshoot a volume with the Failed status, make sure that the underlying physical disk is turned on, plugged in, and attached to the computer. Try returning the disk to the Online status by using the Reactivate Disk command. If this procedure succeeds, the volume automatically restarts and returns to the Healthy status.

If the disk returns to the Online status but the volume does not return to the Healthy status, you can reactivate the volume manually by using the Reactivate Volume command.

In some situations, the Failed status does not indicate data loss even though the Reactivate Disk and Reactivate Volume commands fail. These situations occur when:

• You import a mirrored or RAID-5 volume into a computer running Windows XP Professional or Windows XP Professional x64 Edition. These operating systems do not support mirrored or RAID-5 volumes. You must move the disks back to the original computer to access data on the mirrored or RAID-5 volume.

• You install Windows XP Professional to upgrade a computer that is running Windows NT 4.0 Workstation and that contains multidisk volumes. Because Windows XP Professional cannot access multidisk volumes created by using Windows NT 4.0, you must use Ftonline.exe to return the volumes to Healthy status so that you can access data on them. For more information about managing multidisk volumes during Windows XP Professional Setup, see Chapter 12, “Organizing Disks.” For more information about using Ftonline.exe, click Tools in Help and Support Center and then click Windows Support Tools.

Healthy (At Risk)

The Healthy (At Risk) status occurs when a dynamic volume is experiencing I/O errors caused by bad sectors on the physical disk. The disk remaps the bad sectors by using sectors reserved exclusively for remapping. If the errors are transient, you can use the Reactivate Disk command in Disk Management to return the volume to the Healthy status. If the At Risk status persists, your disk might be failing. Back up the data and replace the disk as soon as possible.

Healthy (Unknown Partition)

The Healthy (Unknown Partition) status occurs when Windows XP Professional or Windows XP Professional x64 Edition does not recognize the System ID of a partition on an MBR disk. Partitions with the Healthy (Unknown Partition) status might be unknown original equipment manufacturer (OEM) partitions or partitions created by operating systems other than Windows or third-party utilities. You cannot format, assign drive letters or drive paths to, or access data on partitions with Healthy (Unknown Partition) status. You can, however, delete these partitions by using Disk Management or the DiskPart command.

Caution If Windows XP Professional recognizes an OEM partition, Disk Management displays the partition as Healthy (EISA Configuration). You cannot use Disk Management to format, delete, assign drive letters or drive paths to, or access data on Healthy (EISA Configuration) partitions. However, you can use DiskPart to delete OEM partitions by using the delete partition command and specifying the override parameter. Deleting an OEM partition can prevent Windows XP Professional from starting.

Windows XP Professional x64 Edition recognizes primary partitions on basic GPT disks and displays them in the Disk Management interface. Windows XP Professional x64 Edition recognizes partitions on GPT disks that use known partition type GUIDs. If Windows XP Professional x64 Edition does not recognize the partition type GUID of a partition, it displays the partition as Healthy (Unknown Partition).

Windows XP Professional x64 Edition recognizes the following partitions on GPT disks but does not display them in Disk Management:

• Microsoft Reserved partition (MSR)

• Logical Disk Manager (LDM) Metadata partition on a dynamic disk

• LDM Data partition on a dynamic disk

Windows XP Professional x64 Edition also recognizes and displays primary partitions, extended partitions, and logical drives on MBR disks.

For more information about the types of partitions that Windows XP Professional recognizes, see “Master Boot Record on Basic Disks” later in this chapter. For more information about the types of partitions that Windows XP Professional x64 Edition recognizes, see “GPT Partition Table Header” later in this chapter. For more information about partitions on GPT disks, see Chapter 12, “Organizing Disks.”

Unknown

The Unknown status occurs when the boot sector for the volume is corrupted and you can no longer access data on the volume. The boot sector might be infected by a virus. For more information about cleaning an infected computer, see “Viruses That Affect the MBR and Boot Sectors” later in this chapter. For more information about repairing boot sectors, see “Repairing Damaged MBRs and Boot Sectors in x86-Based Computers” later in this chapter.

Viruses That Affect the MBR and Boot Sectors

It is always important to take precautions to protect your computer and the data on it from viruses. Many computer viruses exploit the disk structures that your computer uses to start up by replacing, redirecting, or corrupting the code and data that start the operating system.

For more information about the master boot record (MBR) and boot sector on x86-based computers, see “Disk Sectors on MBR Disks” later in this chapter.

MBR Viruses

MBR viruses exploit the master boot code within the master boot record (MBR) that runs automatically when an x86-based computer starts up. MBR viruses are activated when the BIOS activates the master boot code, before the operating system is loaded.

Many viruses replace the MBR sector with their own code and move the original MBR to another location on the disk. After the virus is activated, it stays in memory and passes the execution to the original MBR so that startup appears to function normally.

Some viruses do not relocate the original MBR, causing all volumes on the disk to become inaccessible. If the listing in the partition table for the active primary partition is destroyed, the computer cannot start. Other viruses relocate the MBR to the last sector of the disk or to an unused sector on the first track of the disk. If the virus does not protect the sector that contains the MBR, normal use of the computer might overwrite the MBR, and the system might not restart.

For more information about the master boot code, see “Disk Sectors on MBR Disks” later in this chapter.

Boot Sector Viruses

As with the master boot code, the boot sector’s executable code also runs automatically at startup, creating another vulnerable spot exploited by viruses. Boot sector viruses are activated before the operating system is loaded and run when the master boot code in the MBR identifies the active primary partition and activates the executable boot code for that volume.

Many viruses update the boot sector with their own code and move the original boot sector to another location on the disk. After the virus is activated, it stays in memory and passes the execution to the original boot sector so that startup appears normal.

Some viruses do not relocate the original boot sector, making the volume inaccessible. If the affected volume is the active primary partition, the system cannot start. Other viruses relocate the boot sector to the last sector of the disk or to an unused sector on the first track of the disk. If the virus does not protect the altered boot sector, normal use of the computer might overwrite it, rendering the volume inaccessible or preventing the system from restarting.

How MBR and Boot Sector Viruses Affect Windows XP Professional

Two common ways that a computer can contract an MBR or boot sector virus are: by starting up from an infected floppy disk; or by running an infected program, which causes the virus to drop an altered MBR or boot sector onto the hard disk.

The malicious activity of an MBR or boot sector virus is typically contained after Windows XP Professional starts. If the virus payload (the malicious activity of the virus) does not run during system startup and if the virus does not alter the original MBR or boot sector, Windows XP Professional prevents the virus from self-replicating to other disks.

During normal operation, Windows XP Professional is immune to viruses infecting these disk structures because it accesses physical disks only through protected-mode disk drivers. Viruses typically subvert the BIOS INT 13h disk access routines, which are ignored after Windows XP Professional starts. However, on computers with multiple-boot configurations, such as Windows XP Professional with Microsoft MS-DOS, Microsoft Windows 95, Microsoft Windows 98, or Microsoft Windows Millennium Edition (Me), an MBR or boot sector virus might infect the computer when you are running another operating system. If this happens, Windows XP Professional is vulnerable to damage.

Viruses that execute their payload during startup are a threat to computers that are running Windows XP Professional because the virus executes before Windows XP Professional takes control of the computer. After Windows XP Professional activates the protected-mode disk drivers, the virus cannot copy itself to other hard disks or floppy disks because the BIOS mechanism on which the virus depends is not used for disk access.

Guidelines for Avoiding Viruses

Follow these guidelines to avoid infecting computers with viruses:

1. Install on your system at least one commercial virus-detection program, and use it regularly to check your computers for viruses. Be sure to regularly update the virus signature files. After you install an antivirus program, immediately update the virus signature files from the software manufacturer’s Internet site. Check with the software manufacturer’s documentation for specific instructions.

   Warning It is extremely important that you regularly update your antivirus program. In most cases, antivirus programs are unable to reliably detect and clean viruses of which they are unaware. Most commercial antivirus software manufacturers offer frequent updates. Take advantage of the latest download to ensure that your system is protected with the latest virus defenses.

2. Before you install Windows XP Professional in a multiple-boot configuration, scan the other operating systems for viruses.

3. Back up files nightly or as needed so that damage is minimized if a virus attack does occur.

4. Before opening a file from a floppy disk or before starting a computer from a floppy disk, scan the floppy disk for viruses.

5. Do not open e-mail attachments from unknown senders. Delete the e-mail and attachments immediately.

6. When you receive an unexpected e-mail attachment from someone you know, verify that the sender intended to send you the attachment. Simply scanning the attachment for viruses is not sufficient because a new virus can propagate without the sender’s knowledge. A virus scanner that does not know about the new virus might not catch the virus.

   If the sender did not intend to send you the attachment, permanently delete the e-mail without opening it.

7. Never run a file that has a .vbs or .js file name extension unless you know exactly what it is going to do before you run it.

8. Regularly check the Microsoft Windows Update Web site and the Microsoft Office Update Web site for patches that fix vulnerabilities and provide security enhancements. In addition, independent software vendors (ISVs) might also provide security-related patches for other programs installed on the computer. For more information, see the Windows Update and Microsoft Office Update links on the Web Resources Page at http://www.microsoft.com/windows/reskits/webresources.

9. Configure the security settings in Microsoft Internet Explorer to protect against downloading infected files or malicious scripts. For more information about protecting computers from unsafe software, see Internet Explorer Help.

10. Do not allow users to log on as members of the Administrators group on their own computers because viruses can do more damage if activated from an account with Administrator permissions. Allow users to log on as members of the Users group so that they have only the permissions that are necessary to perform their tasks.

11. Configure Windows Explorer and My Computer to show extensions for known file types, show hidden files and folders, and show protected operating system files. For example, a malicious file with the name Report.doc.vbs appears in Windows Explorer and My Computer as Report.doc unless you deselect the option to hide extensions for known file types. To change these settings, in My Computer, click the Tools menu, click Folder Options, and then click the View tab.

Treating an MBR or Boot Sector Virus Infection

To remove a virus from your computer, use a current, well-known commercial antivirus program that is compatible with Windows XP Professional. In addition to scanning the hard disks on your computer, be sure to scan all floppy disks that have been used in the infected computer, in any other computers, or with other operating systems in an infected multiple-boot configuration. Scan floppy disks even if you believe they are not infected. Many infections recur because one or more copies of the virus were not detected and eliminated.

If the computer is already infected with a boot sector virus and you install Windows XP Professional into a multiple-boot configuration, standard antivirus programs might not completely eliminate the infection because Windows XP Professional copies the original MS-DOS boot sector to a file called Bootsect.dos and replaces it with its own boot sector. The Windows XP Professional installation is not initially infected, but if the user chooses to start MS-DOS, Windows 95, Windows 98, or Windows Me, the infected boot sector is reapplied to the system, reinfecting the computer.

Avoid Using the Fdisk /mbr Command to Treat Viruses

Do not depend on the MS-DOS command Fdisk /mbr, which rewrites the MBR on the hard disk, to resolve MBR infections. Many newer viruses have the properties of both file infector and MBR viruses, so restoring the MBR does not solve the problem if the virus immediately reinfects the system. In addition, running Fdisk /mbr in MS-DOS on a system infected by an MBR virus that does not preserve or encrypt the original MBR partition table permanently prevents access to the lost partitions. If the disk was configured with a third-party drive overlay program to enable support for large disks, running this command eliminates the drive overlay program and you cannot start up from the disk.

Caution Before you use the Fdisk /mbr command, note the following:

• Running Fdisk /mbr is not supported on dynamic disks or GPT disks.

• Running Fdisk /mbr in MS-DOS overwrites only the first 446 bytes of the MBR, the portion known as the master boot code, leaving the existing partition table intact. However, if the signature word (the last two bytes of the MBR) has been deleted, the partition table entries are overwritten with zeros. If an MBR virus overwrites the signature word, access to all partitions and logical volumes is lost.

Avoid Using the Fixmbr Command to Treat Viruses

The Recovery Console, a troubleshooting tool in Windows XP Professional, offers a feature called Fixmbr. However, it functions identically to the Fdisk /mbr command, replacing only the master boot code and not affecting the partition table. For this reason, it is also unlikely to help resolve an infected MBR.

For more information about the Recovery Console, see Appendix C, “Tools for Troubleshooting.” See also article 122221, “How to Protect Boot Sector from Viruses in Windows,” in the Microsoft Knowledge Base at http://support.microsoft.com.

Repairing Damaged MBRs and Boot Sectors in x86-Based Computers

When you start a computer from the hard disk, the BIOS identifies the startup disk and reads the master boot record (MBR). The master boot code in the MBR searches for the active partition on the hard disk. If the first hard disk on the system does not contain an active partition, or if the master boot code cannot locate the boot sector of the system volume so that it can start the operating system, the MBR displays messages similar to the following:

Invalid partition table.
Error loading operating system.
Missing operating system.

If the active partition exists and the master boot record locates the boot sector of the system volume, the master boot code loads the boot sector of the active partition and transfers CPU execution to that memory address. On computers that are running Windows XP Professional, the executable boot code in the boot sector finds Ntldr, loads it into memory, and transfers execution to that file. However, if the boot sector cannot find Ntldr, which is the file that loads the operating system files from the boot volume, Windows XP Professional cannot start. Windows XP Professional might be unable to find Ntldr in these circumstances:

• If Ntldr is moved, renamed, or deleted.

• If Ntldr is corrupted.

• If the boot sector is corrupted.

• If you install Windows XP Professional and then later install any of the following on the same computer: MS-DOS, Windows 95, Windows 98, or Windows NT 4.0. For more information about configuring a multiple-boot system, see Chapter 1, “Planning Deployments.”

Under the preceding circumstances, the computer might not respond to input or might display one of the following messages:

A disk read error occurred. 
NTLDR is missing. 
NTLDR is compressed.

Restoring the MBR

You must repair the MBR if it becomes corrupted and you can no longer access any volumes on that disk. You can use several tools to repair the MBR. Which tool you choose depends on whether the partition table is also damaged and whether you can start Windows XP Professional.

• Use the Recovery Console.

  You can use the fixmbr command in Recovery Console to repair the MBR. You can start Recovery Console by booting from the Windows XP Professional operating system CD; so this troubleshooting method is available even if Windows XP Professional does not start in normal or safe mode. However, you cannot use Recovery Console to repair partition tables that were damaged by viruses or other corruption.

• Use DiskProbe.

  You can use DiskProbe to restore both the MBR and the partition table, but you must have previously backed up this information by using DiskProbe, and you must be able to start Windows XP Professional.

• Use a third-party disk editor.

  You can use a third-party MS-DOS–based, low-level disk editor to repair the partition table if Windows XP Professional does not start. This method is for experienced users only and involves manually editing the partition table.

Using the Recovery Console to Replace the MBR

You can use the fixmbr command in Recovery Console to rewrite the MBR to resolve a corrupted MBR on a startup disk. However, running fixmbr overwrites only the master boot code, leaving the existing partition table intact. If the corruption in the MBR affects the partition table, running fixmbr might not resolve the problem.

Caution Use this command with care because it can damage your partition table if any of the following apply:

• A virus is present and a third-party operating system is installed on the same computer.

• A nonstandard MBR is installed by a third-party disk utility.

• A hardware problem exists.

Caution Run antivirus software before you use the fixmbr command.

To start the computer and use the Recovery Console to replace the MBR

1. Insert the Windows XP Professional Setup CD-ROM into the CD-ROM drive.

2. Restart the computer. If prompted to press a key to start the computer from the CD-ROM, press the appropriate key.

3. When the text-based part of Setup begins, follow the prompts. Press the R key to repair a Windows XP Professional installation.

4. If you are repairing a system that has more than one operating system installed, from the Recovery Console choose the Windows XP Professional installation that you need to repair.

   Note If you press ENTER without typing a number, the Recovery Console quits and restarts the computer.

   The Recovery Console might also show valid installations of Windows NT 4.0. However, the results of attempting to access a Windows NT 4.0 installation can be unpredictable.

5. When prompted, type the Administrator password. If you do not have the correct password, or if the security database for the installation of Windows XP Professional you are attempting to access is corrupted, Recovery Console does not allow access to the local disks and you cannot repair the MBR.

6. To replace the MBR, at the Recovery Console command prompt, type:

   fixmbr

7. Verify whether you want to proceed. Depending upon the location and the cause of the corruption within the damaged MBR, this operation can cause the data on the hard disk to become inaccessible. Press the Y key to proceed, or press the N key to cancel.

Using DiskProbe to Replace the MBR and Partition Table

If you have backed up the MBR by using DiskProbe, you can use it to restore the MBR on any disk that is not used to start the computer. Restoring the backup MBR rewrites the entire sector, including the partition table. However, DiskProbe only runs under Windows XP Professional, Windows 2000, and Windows NT 4.0. It does not run under MS-DOS, Windows 95, Windows 98, or Windows Me.

If the disk that starts Windows XP Professional has a corrupted MBR, Windows XP Professional does not start. Therefore, you cannot use DiskProbe and must use the Recovery Console to replace the MBR.

For more information about restoring backed up MBRs by using DiskProbe, click Tools in Help and Support Center and then click Windows Support Tools.

Using a Third-Party Disk Editor to Replace the Partition Table

Before you can repair the partition table, you must know the exact values to use to re-create the partition table. If you backed up your MBR and partition table by using DiskProbe, and you have the backup available on a floppy disk or on another computer, you can use DiskProbe on a different computer to see the correct values so that you can manually re-create the partition table.

Replacing the Boot Sector

If Ntldr is damaged or missing, or if the boot sector is corrupted, you can resolve either problem by using the Recovery Console.

To start the computer and use the Recovery Console to replace the boot sector

1. Insert the Windows XP Professional Setup CD-ROM into the CD-ROM drive.

2. Restart the computer. If prompted to press a key to start the computer from the CD-ROM, press the appropriate key.

3. When the text-based part of Setup begins, follow the prompts. Press the R key to repair a Windows XP Professional installation.

4. If you are repairing a system that has more than one operating system installed, from the Recovery Console choose the Windows XP Professional installation that you need to repair.

   Note If you press ENTER without typing a number, the Recovery Console quits and restarts the computer.
   The Recovery Console might also show valid installations of Windows NT 4.0. However, the results of attempting to access a Windows NT 4.0 installation can be unpredictable.

5. When prompted, type the Administrator password. If you do not have the correct password, or if the security database for the installation of Windows XP Professional that you are attempting to access is corrupted, Recovery Console does not allow access to the local disks and you cannot replace the boot sector.

6. To replace the boot sector, at the Recovery Console command prompt, type:

   fixboot [drive:]

If you do not specify a drive letter, the Recovery Console replaces the boot sector of the system volume. If you need to replace the boot sector of a volume that is not the system volume, you must specify the appropriate drive letter.

Using a Disk Editor to Replace the Boot Sector

If the boot sector is not from the boot volume on the hard disk, you can use several methods to replace it. If you backed up the boot sector by using DiskProbe, restoring it by using DiskProbe is the fastest method.

If you want to replace the boot sector on an NTFS volume, you have another alternative. When you create or reformat an existing volume as an NTFS volume, NTFS writes a duplicate of the boot sector in the following location:

• At the end of the volume.

On volumes formatted with Windows XP Professional, Windows 2000, and Windows NT 4.0.

• At the logical center of the volume.

On disks formatted with Windows NT 3.51 and earlier.

You can use DiskProbe to locate and copy a duplicate boot sector to the beginning of the volume. There are also third-party M