Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

Associating log subdisks
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.
Warning: 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.
See “Dirty region logging” on page 60.
See “Dirty region logging in cluster environments” on page 472.
Log subdisks are ignored as far as the usual plex policies are concerned, and are
only used to hold the dirty region log.
Warning: The version 20 DCO volume layout includes space for a DRL. Do not use
procedures that are intended for manipulating log subdisks with a volume that
has a version 20 DCO volume associated with it.
See “Preparing a volume for DRL and instant snapshots” on page 318.
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.
255Creating and administering subdisks
Associating log subdisks