Persistent Storage Manager
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NAS 1000s Administration Guide
Other applications for READ/WRITE snapshots: CFOs and auditors can run trial balances to
accounting systems without affecting the actual systems. Prototyping, a new version of a
program, can be installed in a READ/WRITE snapshot and its compatibility within the system
tested with no adverse effects to the primary system.
Always Keep
ALWAYS KEEP snapshots are treated as untouchable by PSM. In a cache file fill situation
PSM will cease writing to the cache file to avoid deleting or corrupting an ALWAYS KEEP
snapshot. A "disk full" error will be returned to the user. ALWAYS KEEP allows the
administrator to set some milestones that are not subject to the automatic deletion routines.
Automated Snapshot Deletion
PSM has a snapshot weighting system (low to highest) that helps set the priority of the
snapshot. This weighting combined with the age of the snapshot determines the order by
which it is deleted by PSM when the cache file fills up.
A key fact to consider is that PSM provides Primary Data Protection automatically. Once set
up, PSM continues to provide Data Protection generating new scheduled snapshots or deleting
older snapshots with little or no input required from system administrators.
Data Recovery
File/Folder/Volume Recovery
PSM facilitates instant data recovery from the stored on-line images. Individual files, groups
of files, folders, groups of folders or complete volumes can be restored. Recovering the data
can be accomplished by the NAS Administrator or the NAS Administrator can give individual
users access to their data for that purpose through file share access over the network.
Security rights and privileges, as well as file and directory attributes, remain in effect as they
were at the time the snapshot was created.
Snapshots and Drive Defragmentation
A drive defragmenter attempts to consolidate files on a drive by reading various parts of the
files and rewriting them to become contiguous on the drive. When volumes are created they
are initially contiguous as possible on the underlying storage units (RAID arrays and LUNs).
If defrag utilities are used on volumes where snapshots exists, snapshots would grow as the
defrag utility moves blocks from one part of the disk to another. PSM disables defrag on
volumes that have current running snapshots to prevent the unnatural growth of the snapshot.
PSM (current versions) is fully compatible with the Windows 2000 system file defrag utility.
On drives upon which snapshots are not installed or are not active, the defrag utility runs
without interruption. If snapshots are active, by design, the drive is automatically marked as
unavailable for defragmentation. In operation, the utility works as designed - providing defrag
on volumes where it is allowed and omitting drives with active PSM Images. There is no user
intervention required. This is consistent with the defragmentation handling of system and
special files and is officially supported by the Microsoft defrag API. In the rare case when an
existing volume requires defrag, disable scheduled snapshots, delete all snapshots on the
volume and defrag the volume. When defrag completes, re-enable scheduled snapshots.
Defrag is only effective when there are NO snapshots active on the volume being defragged.
Summary of Contents for StorageWorks NAS 1000s
Page 38: ...Setup Completion and Basic Administrative Procedures 38 NAS 1000s Administration Guide ...
Page 78: ...User and Group Management 78 NAS 1000s Administration Guide ...
Page 104: ...Folder and Share Management 104 NAS 1000s Administration Guide ...
Page 134: ...UNIX File System Management 134 NAS 1000s Administration Guide ...
Page 166: ...PSM Error Codes 166 NAS 1000s Administration Guide ...