VERITAS Volume Manager 4.1 Administrator's Guide

Creating and Administering Subdisks

Associating Log Subdisks

Chapter 5206

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.

For a description of DRL, see “Dirty Region Logging (DRL)” on page 46.

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 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 disk02-01 with a plex named

vol01-02, which is already associated with volume vol01, use the

following command:

# vxsd aslog vol01-02 disk02-01

You can also add a log subdisk to an existing volume with the following

command:

# vxassist addlog volume disk

This command automatically creates a log subdisk within a log plex on

the speciﬁed disk for the speciﬁed volume.