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220 Creating and administering subdisks
Associating log subdisks
If the volume is enabled, the association operation regenerates data that belongs
on the subdisk. Otherwise, it is marked as stale and is recovered when the
volume is started.
Associating log subdisks
Note: The version 20 DCO volume layout includes space for a DRL. Do not apply
the procedure described in this section to a volume that has a version 20 DCO
volume associated with it. See “Preparing a volume for DRL and instant
snapshots” on page 275 for more information.
Log subdisks are defined and added to a plex that is to become part of a volume
on which dirty region logging (DRL) is enabled. DRL is enabled for a volume
when the volume is mirrored and has at least one log subdisk.
For a description of DRL, see “Dirty region logging” on page 60. Log subdisks are
ignored as far as the usual plex policies are concerned, and are only used to hold
the dirty region log.
Note: Only one log subdisk can be associated with a plex. Because this log
subdisk is frequently written, care should be taken to position it on a disk that is
not heavily used. Placing a log subdisk on a heavily-used disk can degrade
system performance.
To add a log subdisk to an existing plex, use the following command:
# vxsd [-g diskgroup] aslog plex subdisk
where subdisk is the name to be used for the log subdisk. The plex must be
associated with a mirrored volume before dirty region logging takes effect.
For example, to associate a subdisk named mydg02-01 with a plex named
vol01-02, which is already associated with volume vol01 in the disk group,
mydg, use the following command:
# vxsd -g mydg aslog vol01-02 mydg02-01
You can also add a log subdisk to an existing volume with the following
command:
# vxassist [-g diskgroup] addlog volume disk
This command automatically creates a log subdisk within a log plex on the
specified disk for the specified volume.