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Persistent Storage Manager
Note:
the snapshots. Drive defragmentation only operates on volumes formatted with a 4 KB or smaller
allocation size. HP recommends larger allocation cluster sizes to improve performance.
PSM and Backup
Because snapshots are quick to create, it is possible to capture a coherent view of the volume
data with little or no application downtime. Lack of application downtime removes the
traditional backup window or the amount of time taken to back up to offline media. While
many applications must be shut down to capture an accurate backup, snapshots capture a point
in time view of the data that can be used as the source of backup data. Applications can
continue processing against the volume. Therefore, applications may only have to be
interrupted for a few seconds during the snapshot process.
Although snapshots provide a mechanism for backup that does not require downtime, there are
some considerations that should be given when performing backup and restore of a system
using snapshots. HP recommends you review this section prior to establishing backup and
restore policies. Backup and Restore programs are not trivial applications. As such they
require effort to set up and use effectively. Given the nature of these products, it is critical that
any backup and recovery plan be thoroughly tested before use on a live system.
Be sure to use a backup program that is PSM aware and has been certified for operation with
PSM. This is especially true for open file options, system agents, and disaster recovery.
For backup:
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Defragmentation can not be performed if snapshots exist. To defragment a disk, first delete
Caution:
Snapshots are not a replacement for reliable, periodic data backup. If free cache
space becomes critical, snapshots are automatically deleted. See the "Automated Snapshot
Deletion" section. In addition, snapshots are a short term convenience and may reside on
the same physical drives as the data. If something happens to the data drives, the snapshots
are also affected. Read Appendix A for suggestions on how to back up the NAS device.
For base volumes that have snapshots in use or when backing up snapshots, archive bit
resets and incremental backups should not be used. Archive bit resets are recorded as a
change to the data and can fill the cache file with changes. Incremental backups make use
of the archive bit set as well. Note if the snapshot is set to read only the backup will also
fail.
Be careful in the selection of folders, since snapshot folders provide a view into the data
that can result in the backup of multiple views of the data. Forcing the backup to grow
based on the number of snapshots in use.
Junction points should be turned off to prevent the traversal of multiple snapshot
directories of base volume backups.
Junction points should be turned on when backing up a single snapshot. Be sure to pick the
single snapshot and not the root folder. Selecting the root folder will cause multiple
snapshot backups.
NAS 1000s Administration Guide
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