VERITAS Volume Manager 3.5 Administrator's Guide (September 2004)

Understanding VERITAS Volume Manager
SmartSync Recovery Accelerator
Chapter 1 63
Because the database keeps its own logs, it is not necessary for VxVM to
do logging. Data volumes should be configured as mirrored volumes
without dirty region logs. In addition to improving recovery time, this
avoids any run-time I/O overhead due to DRL which improves normal
database write access.
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.
For details of how to configure sequential DRL, see “Adding DRL Logging
to a Mirrored Volume” on page 269.