Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Redo log volume configuration
A redo log is a log of changes to the database data. Because the database does not
maintain changes to the redo logs, it cannot provide information about which
sections require resilvering. Redo logs are also written sequentially, and since
traditional dirty region logs are most useful with randomly-written data, they are
of minimal use for reducing recovery time for redo logs. However, VxVM can
reduce the number of dirty regions by modifying the behavior of its dirty region
logging feature to take advantage of sequential access patterns. Sequential DRL
decreases the amount of data needing recovery and reduces recovery time impact
on the system.
The enhanced interfaces for redo logs allow the database software to inform VxVM
when a volume is to be used as a redo log. This allows VxVM to modify the DRL
behavior of the volume to take advantage of the access patterns. Since the
improved recovery time depends on dirty region logs, redo log volumes should
be configured as mirrored volumes with sequential DRL.
See “Sequential DRL” on page 58.
Volume snapshots
Veritas Volume Manager provides the capability for taking an image of a volume
at a given point in time. Such an image is referred to as a volume snapshot. Such
snapshots should not be confused with file system snapshots, which are
point-in-time images of a Veritas File System.
Figure 1-31 shows how a snapshot volume represents a copy of an original volume
at a given point in time.
Understanding Veritas Volume Manager
Volume snapshots
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