VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Chapter 1, Understanding VERITAS Volume Manager
Dirty Region Logging (DRL)
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If the vxassist command is used to create a dirty region log, it creates a log plex
containing a single log subdisk by default. A dirty region log can also be set up manually
by creating a log subdisk and associating it with a plex. The plex then contains both a log
and data subdisks.
Sequential DRL
Some volumes, such as those that are used for database replay logs, are written
sequentially and do not benefit from delayed cleaning of theDRL bits. For these volumes,
sequential DRL can be used to limit the number of dirty regions. This allows for faster
recovery should a crash occur. However, if applied to volumes that are written to
randomly, sequential DRL can be a performance bottleneck as it limits the number of
parallel writes that can be carried out.
The maximum number of dirty regions allowed for sequential DRL is controlled by the
tunable voldrl_max_seq_dirty as described in the description of
“voldrl_max_seq_dirty” on page 297.
Note DRL adds a small I/O overhead for most write access patterns.
For details of how to configure DRL and sequential DRL, see “Adding DRL Logging to a
Mirrored Volume” on page 197.