Associating Subdisks

Associating a subdisk with a plex places the amount of disk space defined by the subdisk at a specific offset within the plex. The entire area that the subdisk fills must not be occupied by any portion of another subdisk. There are several ways that subdisks can be associated with plexes, depending on the overall state of the configuration.

If you have already created all the subdisks needed for a particular plex, to associate subdisks at plex creation, use the following command:

# vxmake plex plex_name sd=subdisk_name,... 

For example, to create the plex home-1 and associates subdisks disk02-01, disk02-00, and disk02-02 with plex home-1, use the following command:

# vxmake plex home-1 sd=disk02-01,disk02-00,disk02-02 

Subdisks are associated in order starting at offset 0. If you use this type of command, you do not have to specify the multiple commands needed to create the plex and then associate each of the subdisks with that plex. In this example, the subdisks are associated to the plex in the order they are listed (after sd=). The disk space defined as disk02-01 is first, disk02-00 is second, and disk02-02 is third.

This method of associating subdisks is convenient during initial configuration. Subdisks can also be associated with a plex that already exists. To associate one or more subdisks with an existing plex, use the following command:

# vxsd assoc plex_name sd_name [sd_name2 sd_name3 ...]

For example, to associate subdisks named disk02-01, disk02-00, and disk02-02 with a plex named home-1, use the following command:

# vxsd assoc home-1 disk02-01 disk02-00 disk02-01 

If the plex is not empty, the new subdisks are added after any subdisks that are already associated with the plex, unless the -l option is specified with the command. The -l option associates subdisks at a specific offset within the plex.

The -l option is needed when you create a sparse plex (that is, a plex with a gap between its subdisks) for a particular volume, and want to make this plex complete. To make the plex complete, create a subdisk of a size that fits the hole in the sparse plex exactly. Then, to associate the subdisk with the plex by specifying the offset of the beginning of the hole in the plex, use the following command:

# vxsd -l offset assoc sparse_plex_name exact_size_subdisk

	NOTE: The subdisk must be exactly the right size because Volume Manager does not allow for the space defined by two subdisks to overlap within a single plex.

For striped subdisks, to specify a column number and column offset for the subdisk, use the following command:

# vxsd -l column_#/offset assoc plex_name sd_name ...

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.

Associating Log Subdisks

Log subdisks are defined for and added to a plex that is to become part of a volume using Dirty Region Logging. Dirty Region Logging is enabled for a volume when the volume is mirrored and has at least one log subdisk.

For a description of Dirty Region Logging, see “Dirty Region Logging”, and “Dirty Region Logging and Cluster Environments”. 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 as a log subdisk. The plex must be associated with a mirrored volume before DRL 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

	NOTE: You can also add a log subdisk to an existing volume with the following command: # vxassist addlog volume_name disk This command automatically creates a log subdisk within a log plex for the specified volume.