Planning a Fault-Tolerant Disk Configuration
A redundant array of independent disks (RAID) is a fault-tolerant disk configuration in which part of the physical storage capacity contains redundant information about data stored on the disks. The redundant information is either parity information (in the case of a RAID-5 volume), or a complete, separate copy of the data (in the case of a mirrored volume). The redundant information enables regeneration of the data if one of the disks or the access path to it fails, or a sector on the disk cannot be read. Windows 2000 Server implements these fault-tolerant configurations in its software. Use Disk Management, shown in Figure 11.1, to configure mirrored volumes and RAID-5 volumes, and to reconstruct the volume when there has been a failure.
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Note
You can also use hardware RAID arrays.
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Figure 11.1 Disk Management
Table 11.2 shows the volume status descriptions that appear in the graphical view of the volume and in the Status column of the volume in List view.
Table 11.2 Disk Management Volume Status Descriptions
Volume Status |
Description |
|---|---|
Healthy |
The volume is accessible and has no known problems. This is the normal volume status. No user action is required. Both dynamic volumes and basic volumes display the Healthy status. |
Healthy (At Risk) |
The dynamic volume is currently accessible, but I/O errors have been detected on the underlying disk. If an I/O error is detected on any part of a disk, all volumes on the disk display the Healthy (At Risk) status. Only dynamic volumes display the Healthy (At Risk) status. |
Initializing |
The dynamic volume is being initialized. Only dynamic volumes display the Initializing status. |
Resynching |
The volume's mirrors are being resynchronized so that volume mirrors contain identical data. |
Regenerating |
Data and parity are being regenerated for the RAID-5 volume. |
Failed Redundancy |
The data on the volume is no longer fault tolerant because one of the underlying disks is not online. The Failed Redundancy status applies only to mirrored or RAID-5 volumes. |
Failed Redundancy (At Risk) |
The data on the volume is no longer fault tolerant and I/O errors have been detected on the underlying disk. If an I/O error is detected on any part of a disk, all volumes on the disk display the (At Risk) status. Only dynamic mirrored or RAID-5 volumes display the Failed Redundancy (At Risk) status. |
Failed |
The volume cannot be started automatically. Both dynamic and basic volumes display the Failed Status. |
Missing |
A dynamic disk is corrupted, powered down, or disconnected. |
Certain disk subsystems implement RAID technology completely within the hardware. Some of these hardware implementations support hot swapping of disks, which enables you to replace a failed disk while the computer is still running Windows 2000 Server. A ** RAID array is a fault-tolerant disk subsystem where all of the fault tolerance is implemented by the hardware. For information about RAID arrays that are compatible with Windows 2000, see the Windows 2000 Hardware Compatibility List (HCL) link on the Web Resources page at https://windows.microsoft.com/windows2000/reskit/webresources .
All RAID disk configurations regenerate data to satisfy read requests when a disk or a path to a disk has failed. Regeneration involves reading data from other disks in the volume. RAID disk configurations also reconstruct the missing data onto the new disk when you have replaced the failed disk (or the path to it). When you have implemented a fault-tolerant volume, use Disk Management reconstruct the data. If you are using a RAID array, see the vendor's documentation for information about reconstructing data.
Configuring mirrored volumes and RAID-5 volumes is discussed later in this chapter. For more information about recovering from failures of mirrored volumes and RAID-5 volumes, see "Repair, Recovery, and Restore" in this book.