Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Adding Traditional DRL Logging to a Mirrored Volume
242 VERITAS Volume Manager Administrator’s Guide
You can also specify vxassist-style storage attributes to define the disks that
can or cannot be used for the plexes of the DCO volume.
Note The vxsnap prepare command automatically enables FastResync on the volume
and on any snapshots that are generated from it.
If the volume is a RAID-5 volume, it is converted to a layered volume that can be
used with snapshots and FastResync.
Adding Traditional DRL Logging to a Mirrored Volume
Note The procedure described in this section creates a DRL log that is configured within a
dedicated 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. However, a version 20
DCO volume cannot be used in conjunction with a separate DRL plex. For full
details, see “Preparing a Volume for DRL and Instant Snapshots” on page 235.
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]
Note 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]