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.

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.

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.

More Information

Dirty region logging

Dirty region logging in cluster environments

Preparing a volume for DRL and instant snapshots