Follow these 11 tips to increase restore performance

TSM offers many features and techniques to improve the client node restore performance. Following these recommended best practices would help you to reduce the time for restoration. Different TSM setups may require different techniques based up on their Storage and Network configuration. In this post I will discuss some of the IBM recommended techniques to improve your restore performance. You should select appropriate techniques suitable for your TSM environment. 

Most of the TSM administrators choose daily incremental backups and weekly/monthly full backups to reduce the backup time and tape resources. As days goes by, the data will not be closely packed together in relevant tape volumes since active data will be mixed in with inactive data, expired data and data from other nodes/filespaces that are not relevant to a particular restore operation. So, eventually a simple single directory restore will become more problematic & time consuming because data is unevenly located in the tapes.

Initially performance will be good, however over time as the data is spread out over a tape or multiple tapes performance becomes degraded. The degradation is caused by the increase in tape locate commands that are used to get to the valid data and perhaps additional tape mounts. Tape drives perform well when they are allowed to stream, reading or writing sequential data, but when forced to skip around on the tape the locate commands begin to dominate.

Tivoli Storage Manager Restore Process
In TSM, there are three basic types of Restore scenarios

Single file Restore
TSM is optimized very well for this type of scenario since TSM keeps records of the exact location of each file

Multiple file (directory) Restore
Initially this scenario will be fast but slowly it will become problematic since the required directory (or set of files) may be spread throughout a tape or set of tapes over time

Total file system Restore 
Total file system restoration is mostly done during Disaster recovery or during changing to new hardware. This scenario  can be optimized if image backup/restore is utilized.

Also Read: TSM Administrator Daily routine tasks

Based upon your environment and requirements you should plan your backup strategy to include image backup and some occasional selective/full backups along with daily incremental backups.

How to improve TSM Client Restore Performance

There are several methods that can help avoid the problem of slow restore. Many of these below mentions techniques and strategies can and should be used together, whereas others are mutually exclusive.

Also Read: Why is it important to use DIRMC option during backups ?

1. Understand when to use No Query Restore and Classic Restore
TSM utilizes two different types of methods when determining what needs to be restored based on the restore specification used, NQR and classic restore.

NQR is invoked when a simple wildcard, which matches an entire directory, is used such as:

Classic Restore invokes when the options “inactive”, “latest”, “pick”, “fromdate”, and “todate” are not used. A restricted wildcard that matches a subset of files in a directory such as:

The difference becomes important because the two types have different performance characteristics. When restoring an entire filesystem, NQR will be superior. However when restoring a single directory classic restore can be faster in some situations. Classic restore can be invoked in these situations by using a (trick) slightly different wildcard such as (?*)

Classic restore can also be invoked by using the testflag DISABLENQR. If small restores are taking too much time, classic restore may provide better performance. The difference becomes more pronounced for large filesystems with millions of files.

2. Use Multiple Sessions Restore
Multi-session restore allows TSM to restore data from multiple tape volumes simultaneously if the desired data resides on multiple tapes, increasing performance.

If collocation by node or filespace is being used client data may only reside on one tape, eliminating the possibility of using multi-session restore.

Also Read: TSM Server Performance Tuning Parameters

3. Configure appropriate Collocation Mode
TSM Collocation when enabled reserves a volume or set of volumes for a particular TSM client, filespace or group of clients. This allows filespace data to be more closely packed together and avoids excessive tape mounts. It’s possible that dozens of tapes could be needed for restore of a single filespace or even a directory with collocation disabled. Collocation can be enabled for nodes, groups of nodes, or filespaces.

Using collocation will results in increased tape cartridge use and the fact that multi-session restore may not be used effectively since data may reside on a single tape volume. However using collocation by group can eliminate these drawbacks if groups are chosen wisely such that the total quantity of data stored by a particular group is able to fill several tape volumes.

4. Perform weekly/Monthly Full Selective backups of Filesystems
Similar to image backup, a full selective backup of a filesystem has the effect of putting the filesystem data in one place, which provides faster restores. This is the single best way to optimize restore of a subset of a filesystem (directory) when using tape devices.

Periodic selective backups have the drawback of sending all the data when only a fraction may have changed and can interfere with expiration/retention policies.

Also Read: Full vs Differential vs Incremental vs Progressive Incremental Backups 

To minimize the impact of backing up all the data during a particular backup the selective backups for different filespaces/nodes can be staggered throughout the week.

To avoid interfering with expiration/retention policies the selective backups can be performed under a different node name. When a restore of a directory or whole filesystem is needed, the last selective can be restored under the alternate node name, and then any changed files since that selective can be restored from the incremental backups, similar to what is done for image backup, except a single directory restore is possible. For restore of an entire filesystem, image backup/restore is superior.

5. Perform Periodic Image Backups
Image backup can be used to take a snapshot at the disk device level, which provides high back up and restore speeds since individual files need not be processed. Image backup is most often integrated with the incremental forever strategy. Incremental backups are performed often and image backups performed less often, depending on how much the data is changing. If most of the data is changing between image backups the benefit of image restore becomes less to none.

Also Read: Different types of Incremental Backups

Upon a full filesystem failure the image can be restored at great speed and then the files that changed between the time that image was taken and the last incremental are then restored. This has the advantage of allowing the drive to stream during the image restore and has the added advantage that the files restored since the image are likely to be closely packed together (since they were backed up relatively recently.)

6. Running regular Tape Reclamation
Be sure that tape reclamation is running periodically (storage pool reclaim < 100%.) By freeing up unused areas of tape reclamation makes data more compact on the tape volume, providing better restore performance.

7. Run/Start Multiple Restore Commands
When restoring multiple filespaces start one restore command for each filespace to allow them to happen simultaneously. This has the greatest effect if the node’s data is collocated by filespace.

Also Read: Restoring damaged Storagepool volumes

8. Use Virtual Mountpoints
When filesystems becomes large or huge,  virtual mount points can be used to make a single filesystem appear as many to TSM. This is only possible if the directory structure is somewhat static and balanced. Through collocation you can then ensure that different parts of the filesystem go to different tapes allowing a more optimized restore.

9. In Disaster Recovery Situations Use “Move Data” or “Move Nodedata” Commands To Stage Data To Disk
In a DR situations, time will be needed to physically get the client system back online. Client data can be restored to a disk storage pool from primary tape pool volumes so that when the client system becomes available much, or all, of the data can be restored from disk. This can be done by using MOVE DATA or MOVE NODEDATA commands.

Also Read: TSM Storage Pool Concepts (V7 Revised)

10. Prioritize Importance of Nodes
Important nodes can be put in a separate storage pool that uses tape collocation, utilizes disk as main storage, or uses other features that you may not be willing to use for all clients.

11. Utilize Active Data Pools
Active data pools allow your most recent data to reside on disk while older, inactive data may be stored on tape. Most restores are of the active data and if that data is in an active data pool on disk restores may be much faster. 

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