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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 59.

See "Dirty region logging in cluster environments" on page 419.

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 284.

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.