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A traditional DRL log is configured within a DRL plex. However, a version 20 DCO volume cannot be used in conjunction with a DRL plex. The version 20 DCO volume layout includes space for a DRL log. The new DCO volume layout also supports traditional (third-mirror), instant (copy-on-write), and instant space-optimized snapshots.
See "Preparing a volume for DRL and instant snapshots" on page 284.
To put dirty region logging (DRL) into effect for a mirrored volume, a log subdisk must be added to that volume. Only one log subdisk can exist per plex.
To add DRL logs to an existing volume, use the following command:
# vxassist [-b] [-g diskgroup] addlog volume logtype=drl \ [nlog=n] [loglen=size]
If specified, the -b option makes adding the new logs a background task.
The nlog attribute can be used to specify the number of log plexes to add. By default, one log plex is added. The loglen attribute specifies the size of the log, where each bit represents one region in the volume. For example, the size of the log would need to be 20K for a 10GB volume with a region size of 64 kilobytes.
For example, to add a single log plex for the volume vol03, in the disk group, mydg, use the following command:
# vxassist -g mydg addlog vol03 logtype=drl
When the vxassist command is used to add a log subdisk to a volume, by default a log plex is also created to contain the log subdisk unless you include the keyword nolog in the layout specification.
For a volume that will be written to sequentially, such as a database log volume, include the logtype=drlseq attribute to specify that sequential DRL is to be used:
# vxassist -g mydg addlog volume logtype=drlseq [nlog=n]
Once created, the plex containing a log subdisk can be treated as a regular plex. Data subdisks can be added to the log plex. The log plex and log subdisk can be removed if this is required.
See "Removing a traditional DRL log" on page 291.