VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Chapter 5, Creating and Administering Subdisks

Associating Log Subdisks

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Note The subdisk must be exactly the right size. VxVM does not allow the space deﬁned

for two subdisks to overlap within a plex.

For striped or RAID-5 plexes, use the following command to specify a column number

and column offset for the subdisk to be added:

# vxsd -l column_#/offset assoc plex subdisk ...

If only one number is speciﬁed with the -l option for striped plexes, the number is

interpreted as a column number and the subdisk is associated at the end of the column.

Alternatively, to add M subdisks at the end of each of the N columns in a striped or

RAID-5 volume, you can use the following form of the vxsd command:

# vxsd assoc plex subdisk1:0 ... subdiskM:N-1

The following example shows how to append three subdisk to the ends of the three

columns in a striped plex, vol-01

# vxsd assoc vol01-01 disk10-01:0 disk11-01:1 disk12-01:2

If a subdisk is ﬁlling a “hole” in the plex (that is, some portion of the volume logical

address space is mapped by the subdisk), the subdisk is considered stale. 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

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 adescription of DRL, see “Dirty Region Logging(DRL)” on page 40. Logsubdisks 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.