Note on IT

Published: May 20, 2004 | Updated: December 1, 2004

The Microsoft IT group backs up its clustered Microsoft® Exchange Server 2003 mailbox infrastructure by using a modified version of the Backup feature in Microsoft Windows Server™ 2003. The modifications enable Microsoft IT to increase throughput and back up the data faster, thereby meeting service level agreements (SLAs) despite the very large quantity of data backed up nightly.

Introduction

The Microsoft IT group uses a two-stage process to complete the backup requirements in its clustered Exchange Server 2003 environment.

The process is discussed at a high level in the IT Showcase technical case study "Messaging Backup and Restore at Microsoft,". The IT Showcase white paper Exchange 2003 Design and Architecture at Microsoft also includes a discussion on this topic.

This document defines the setup process and server optimizations required to complete the Exchange Server 2003 backup process that Microsoft IT uses. This document assumes that readers are either Exchange architects or technical implementers and are already familiar with Exchange Server 2003, Windows Server 2003 clusters, and Exchange server backup procedures.

Note   For security reasons, the sample names of forests, domains, internal resources, organizations, and internally developed applications and files used in this document do not represent actual names used within Microsoft and are for illustration purposes only. In addition, the contents of this document describe how Microsoft IT runs its enterprise data center. The procedures and processes included in this document are not intended to be prescriptive guidance on how to run a generic data center and may not be supported by Microsoft Customer Support Services.

Cluster Setup

The setup steps for clusters are based on the assumption that the Exchange storage groups and mail stores already exist. The initial steps require some specific cluster configurations to allow for disk resource movement between nodes without affecting the Exchange clustered resources.

Naming of Clustered Servers

Microsoft IT uses a multi-node clustered design in which the largest cluster configuration contains seven nodes. There are four active (A) nodes, one primary passive (P) node, and two alternate passive (p) nodes. Such a cluster is abbreviated as AAAAPpp. Each node configuration provides a different level of functionality specifically to support the backup process.

Servers in the Exchange server clusters are named through a specific, three-part naming convention—xxx-yyyy-n—to allow for easy recognition of server roles. In this naming convention:

• The xxx part represents the geographic location of the server.
• The yyyy part identifies the default role of the server in the cluster.
• The n part is the numeric representation of the server within the cluster.

Although the geographic location code is arbitrary to this discussion, clearly identifying the server roles is necessary for promoting an understanding the Microsoft IT Exchange server backup process. Table 1 lists the role definitions.

Table 1   Roles of Servers in an Exchange Server Cluster

For example, the second active node in an Exchange server cluster located in a Texas data center would be named TEX-ACTV-2.

Naming of Cluster Resource Groups

A resource group is a movable entity of resources within a cluster. Resources within a group can be moved within the cluster independently of other resource groups.

The cluster is configured to support multiple resource groups through a three-part naming convention similar to the server naming convention—xxx-zzzz-n—to allow for easy recognition of resource group functions. Each resource group in a cluster represents a virtual server for that cluster. In this naming convention:

• The xxx part represents the geographic location of the Exchange instance.
• The zzzz part identifies the role of the Exchange instance.
• The n part is the numeric representation of the Exchange instance within the cluster.

Clearly identifying the resource group roles is also necessary for understanding the Microsoft IT Exchange server backup process. Table 2 lists the role definitions.

Table 2   Roles of Resource Groups in an Exchange Server Cluster

For example, the first mailbox resource group in an Exchange server cluster located in a Texas data center would be TEX-MAIL-1.

Cluster Layout

In the Microsoft IT configuration, each cluster contains its own resource groups (defined by role) and server names (defined by default status). Each of the four active-node servers has its own MAIL resource group and BACK resource group. The resource group layout used is required for supporting the two-stage backup process that Microsoft IT uses.

Custom Backup Configurations

To accomplish its backup process, Microsoft IT customized the configuration of the built-in Backup feature of Windows Server 2003 by modifying the registry, creating backup selection files, and creating backup scripts.

Modifying the Registry

The following steps detail how Microsoft IT implemented specific registry modifications that optimized the data throughput of the built-in Backup engine:

Warning   Incorrectly editing the registry can have serious, unexpected consequences that can prevent the system from starting and require you to reinstall Microsoft Windows®. A recommended best practice is to export the subkey before editing it. You can also set a System Restore point prior to using Registry Editor.

1. Start a Remote Desktop Connection session to xxx-ACTV-0 by using an account that will be assigned to support the scheduled tasks for Backup. The account will need, at a minimum, Exchange View only administrator user rights and must be a member of the Backup Operators group on each node within the cluster.
2. Start Regedit.exe, and then browse to HKEY_CURRENT_USER\Software\Microsoft\Ntbackup.

   Note   There will be subkeys at this location in the registry only if the Backup feature was previously run to back up data on the computer. If subkeys exist, skip to step 4; if subkeys do not exist, continue with the next step.

3. Start Backup, and then back up a single, small file to disk. This action will cause Backup to create the necessary registry entries. After Backup has finished, you can delete the backed-up file that you created. Close Backup.
4. Expand HKEY_CURRENT_USER\Software\Microsoft\Ntbackup to reveal the subkeys.
5. Browse to the HKEY_CURRENT_USER\Software\Microsoft\Ntbackup\Backup Engine subkey.
6. Edit the value of the entry Logical Disk Buffer Size from 32 to 64.
7. Edit the value of the entry Max Buffer Size from 512 to 1024.
8. Edit the value of the entry Max Num Tape Buffers from 9 to 16.
9. Close Regedit.exe.

Creating Backup Selection Files

Microsoft IT uses all four available storage groups for a total of 20 mail database stores per Exchange virtual instance. The sizes of Microsoft IT's mail database stores average 30–50 gigabytes (GB). Based on both the sizes of its mail database stores within the storage group and the goal to optimize the time needed for the data recovery process, Microsoft IT backs up Exchange at the mail database store level rather than the storage group level. More specific reasons for backing up this way include:

• It reduces the size of the .bkf flat file created during the backup process on disk. A storage group backup would produce one ~200-GB flat file, whereas a mail database store backup would produce multiple ~30-GB to ~40-GB files (one per mail store). The time savings of using a mail database store backup is significant because if an error occurs when streaming this content to tape, the retry occurs with a ~30-GB to ~40-GB file rather than a ~200-GB file.
• It allows for running more concurrent jobs when streaming to tape (one scheduled job per flat file), depending on the number of tape devices available to process requests.

However, it must be noted that backing up by mail store rather than by storage group makes recovery more complicated in the event that an entire storage group has to be recovered due to log replay requirements. Other IT organizations who manage smaller mail stores may choose to perform storage group backups for its comparative simplicity.

The following steps can be used to create a preconfigured storage group backup job for each storage group:

1. Start a Remote Desktop Connection session to xxx-ACTV-0 by using an account assigned to support the scheduled tasks for Backup.
2. Start Backup.
3. Click the Backup tab.
4. Expand Microsoft Exchange Server – xxx-MAIL-0 in this example.
5. Expand Microsoft Information Store.
6. Select the first storage group.
7. Click the Job menu, and then click Save Selection As.
8. Type SG1 for the file name (as an example for the first storage group), and then click Save to store the file to the default folder on disk: C:\Documents and Settings\user_name\Local Settings\Application Data\Microsoft\Windows NT\NTBackup\data. The user name in this path is for the account referenced in step 1.
9. Cancel the selection of the first storage group.
10. Repeat steps 6 through 9 for the remaining storage groups by using SG2, SG3, and SG4 for the corresponding storage groups if required.

The goal of these steps is to create the Backup selection files (.bks) for each storage group.

Note   Never modify the selection files after they are created, or they will be rendered useless and will have to be re-created through the preceding steps.

Creating Backup Scripts

Microsoft IT created command-prompt backup scripts for its full nightly backup jobs. The following command-prompt statements were collected in the Sg1.cmd file to back up the first storage group. The command file automatically re-enabled the relevant registry modifications for the Backup feature to ensure optimized throughput.

reg add "HKCU\Software\Microsoft\Ntbackup\Backup Engine" /v 
"Logical Disk Buffer Size" /t REG_SZ /d 64 /f
reg add "HKCU\Software\Microsoft\Ntbackup\Backup Engine" /v 
"Max Buffer Size" /t REG_SZ /d 1024 /f
reg add "HKCU\Software\Microsoft\Ntbackup\Backup Engine" /v 
"Max Num Tape Buffers" /t REG_SZ /d 16 /f 
C:\%OS%\system32\Ntbackup.exe backup "@C:\Documents and 
Settings\user_name\Local Settings\Application 
Data\Microsoft\Windows NT\NTBackup\data\Sg1.bks" /n "SG1" /d 
"SG1" /v:no /r:no /rs:no /hc:off /m normal /j "SG1" /l:s /f 
U:\Sg1.bkf"

Note   Ntbackup.exe is the command line executable program file that provides the services associated with the Backup feature.

The following are definitions for the subset of command-prompt switches used with Ntbackup.exe in the preceding example:

• /d "set description" (specifies a label for each backup set)
• /f "file name" (specifies path and file name of .bkf file)
• /hc:[on/off] (uses hardware compression)
• /j "job name" (specifies job name used in log file)
• /l:[f/s/n] (specifies log file summary type: full, summary, or none)
• /m "[normal/copy/differential/incremental/daily]" (specifies type)
• /n "media name" (specifies new media name)
• /r:[yes/no] (restricts access to owner or Administrators group)
• /rs:[yes/no] (uses remote storage)
• /v:[yes/no] (verifies data after backup is complete)

Note   For a complete list of command-prompt switches and their definitions, see the Ntbackup Web page.

Microsoft IT created additional .cmd files to reference the other selection files for SG2, SG3, and SG4. These .cmd files were created without the registry modification references. Microsoft IT then copied all backup .cmd files to a folder designated for storing them.

Creation of Scheduled Tasks

Microsoft IT uses the Scheduled Tasks application to automate the nightly full backup process.

Creating Schedules for Backup Jobs

Microsoft IT uses the following procedure to set up the scheduled tasks to run the backup jobs:

1. Start a Remote Desktop Connection session to xxx-ACTV-0 by using an account assigned to support the scheduled tasks for backup.
2. Click Start, point to All Programs, point to Accessories, point to System Tools, and then click Scheduled Tasks to start the application.
3. Click File, and then click New to create a blank scheduled task (use a name such as SG1).
4. Open the properties of the new scheduled task, and then type the path of the Sg1.cmd file created earlier.
5. Set the account details and password under which the new scheduled task will run. Use the same account used during step 1.
6. Click the Schedule tab, and then define a start time. For example, use 8:00 PM for the first backup job (SG1).
7. Click OK to save the modifications to the scheduled task.
8. Create new scheduled tasks for the remaining storage group backup jobs. Schedule backup jobs for SG2, SG3, and SG4 to start five minutes after SG1 to ensure that the registry modifications for Backup are in place.

Creating Move Schedules for Cluster Resource Groups

Microsoft IT creates move schedules for cluster resource groups. This action ensures that the BACK resource group is active on the same node as the MAIL resource group for the start of the schedule for the first stage, disk-to-disk backup.

The use of these scheduled tasks ensures that the xxx-BACK-0 group is moved between active and alternate passive nodes to process the first-stage and second-stage backups.

To create a scheduled task that will move xxx-BACK-0 to the active node:

1. Start a Remote Desktop Connection session to xxx-ACTV-0 by using an account assigned to support the scheduled tasks for backup.
2. Start Scheduled Tasks.
3. Create a new scheduled task called MoveACTV.
4. Open the properties of the schedule, and then type C:\Windows\system32\cluster.exe group xxx-BACK-0 /move:xxx-ACTV-0 in the Run box.
5. Set the account details and password under which the new scheduled task will run. This account should be the same account used during step 1.
6. Click the Schedule tab, and then define a start time. For example, use 7:00 PM to ensure that the move is completed prior to the 8:00 P.M. scheduled backup.

To create a scheduled task that will move xxx-BACK-0 to an alternate passive node:

1. Create a new scheduled task called MovePASS.
2. Open the properties of the schedule, and then type C:\Windows\system32\cluster.exe group xxx-BACK-0 /move:xxx-PASS-2 in the Run box.
3. Set the account details and password under which the new scheduled task will run. This account should be the same account used during step 1.
4. Click the Schedule tab, and then define a start time. For example, use 1:30 AM to allow enough time for the 8:00 P.M. scheduled backup to be completed.

Note   There is no automation in place to monitor the end time of the first stage, disk-to-disk backup. The process needs to be monitored manually to ensure that the resource groups are not removed before the disk-to-disk backup is completed.

Issues

Microsoft IT encountered one key issue that needed to be resolved before the solution was ready to be implemented.

Using the version of the Backup feature included with Windows Server 2003, Microsoft IT detected a reduction in sustainable throughput over a 20-minute period. A cache contention issue caused the reduction in throughput. This issue was further aggravated by the increased backup throughput available as a result of the registry modifications to the Backup engine.

Microsoft IT noticed a negative trend in performance when running four concurrent backups (one per storage group). Processor utilization increased over time, and a corresponding increase occurred in processor utilization on the system process. These increases correlated to a simultaneous decrease in sustainable throughput. All of these situations can be detected by means of performance monitoring.

To eliminate the cache contention problem, Microsoft IT used a revised version of Backup that provides a new command-prompt switch. The switch enables a "file unbuffered" setting to bypass the cache manager. This change provides a number of benefits during the disk-to-disk backup process:

• Sustainable throughput over time
• Reduction in processor utilization—peak utilization reduced to 30 percent on average
• Elimination of impacts to the system process during the backup job

The revised version of Backup that supports the file unbuffered (/fu) switch is targeted for general delivery with Service Pack 1 for Windows Server 2003. However, the revised version of Ntbackup.exe can be directly downloaded as a hotfix through the Microsoft Knowledge Base article "System performance is negatively affected when Ntbackup.exe writes to a destination .bkf file".

For users who have deployed the revised version of Ntbackup.exe, the last line of the backup script defined earlier in this document should be modified to include the /fu switch. A modified example of that command is as follows:

C:\%OS%\system32\Ntbackup.exe backup "@C:\Documents and 
Settings\user_name\Local Settings\Application 
Data\Microsoft\Windows NT\NTBackup\data\Sg1.bks" /n "SG1" /d 
"SG1" /v:no /r:no /rs:no /hc:off /fu /m normal /j "SG1" /l:s 
/f U:\Sg1.bkf"

To illustrate the dramatic improvement in backup performance associated with the use of the /fu switch, a pair of System Monitor screenshots were taken of an Exchange mailbox server running Ntbackup.exe. The first image shows the server running Ntbackup.exe without using the /fu switch. As shown in Figure 1, the disk write bytes per second (white line) performance of Ntbackup.exe continually degraded over time while the processor utilization associated with the System process (pink line) quickly spiked to and remained at 100 percent. This resulted in the total processor utilization (red line) starting relatively high and continued to increase for the duration of the backup.

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Figure 1   Running Ntbackup.exe without the /fu switch

On the same server backing up the same data while working under the same load, the /fu switch was added to the backup script and a second System Monitor screenshot was snapped, as shown in Figure 2.

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Figure 2   Running Ntbackup.exe with the /fu switch

In contrast to the previous image, Figure 2 shows how the disk write bytes per second (white line) performance of Ntbackup.exe immediately achieved a much higher level and maintained that level throughout the backup process. The processor utilization associated with the System process (pink line) started near zero and was largely unaffected by running Ntbackup.exe. This resulted in the total processor utilization (red line) starting relatively low and maintained that same level for the duration of the backup.

Findings and Recommendations

The optimizations and throughputs that Microsoft IT received in its two-stage backup process are based on its specific hardware platform that was tuned for optimized throughput. Microsoft IT recommends that any enterprise that is planning an Exchange deployment should perform an investigation during the infrastructure design stage to determine the optimized throughput of a proposed storage solution. The findings of Microsoft IT include the following:

• Using the updated version of Ntbackup.exe enables the use of the new /fu switch, which increases initial throughput and sustains it over time with a substantial reduction in processor utilization without impact upon the System process.
• Individual backup throughput per storage group can be sustained at approximately 1.2 GB per minute.
• Total throughput can be sustained at approximately 4.8 GB per minute per Exchange virtual server with four concurrent backups running.
• Some storage area network (SAN) enclosures may not be able to support such high levels of sustained throughput. The enclosure used by Microsoft IT sustains between 6 GB and 7 GB per minute, which enables Microsoft IT to run eight concurrent backups across two Exchange virtual servers per SAN.
• Sustainable throughput should be monitored through System Monitor in Windows Server 2003 for the disk-to-disk backup process during testing stages. Specifically, the Total Disk Write Bytes/Sec performance counter should be monitored.
• Throughput to tape can be sustained at a rate of 1.6 GB per minute per stream with up to four concurrent streams to four LTO1 tape devices, as validated in production.
• Microsoft IT achieved best throughput by having ample Logical Unit Number (LUN)-to-SAN controller distribution that uses a third-party multipath software solution. Microsoft IT's configuration uses the following design:
  • SG1 and SG2 data, log, and backup disks per virtual server on controller 1
  • SG3 and SG4 data, log, and backup disks per virtual server on controller 2
• Restore rates can be achieved in the range of 2 GB per minute for a disk-to-disk-based restoration. This throughput is achievable once the disks being written to are not under any form of production load.
• Microsoft IT configured the backup target disks by using redundant array of independent disks level 5 (RAID 5) as a cost-effective use of disk resources.
• Microsoft IT disabled mirrored write-back cache on all backup targets to eliminate a potential degradation of disk write performance.

  Note   This setting is specific to HP StorageWorks Enterprise Virtual Array 5000, the storage enclosure deployed by Microsoft IT.

• Microsoft IT modified the starting sector on all backup target disks to eliminate the offset on primary partitions as a result of the default master boot record (MBR) structure to improve disk performance. Microsoft IT recommends the use of the Windows 2000 Server Resource Kit tool Diskpar.exe to partition LUN volumes to achieve this configuration.
• Microsoft IT strongly advises against the sharing of disk spindles to support backup targets and Exchange databases. Following this as a best practice helps ensure that sequential content streaming to tape does not adversely affect the random access requirements for Exchange. Following this recommendation enables Microsoft IT to stream the backup content to tape as part of the second-stage process at any time during the day without affecting users supported on the clusters.

For More Information

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