HP Veritas Volume Manager 5.0 -UX 11i v3 Adding traditional DRL logging to a mirrored volume, Preparing a volume for DRL and instant snapshots, Adding traditional DRL logging to a mirrored volume

Administering volumes 281

Adding traditional DRL logging to a mirrored volume

subsequently create from the snapshot plexes. For example, specify ndcomirs=5 for a volume with 3 data plexes and 2 snapshot plexes. The value of the regionsize attribute specifies the size of the tracked regions in the volume. A write to a region is tracked by setting a bit in the change map. The default value is 64k (64KB). A smaller value requires more disk space for the change maps, but the finer granularity provides faster resynchronization.

To enable DRL logging on the volume, specify drl=on (this is the default setting). If sequential DRL is required, specify drl=sequential.If DRL is not required, specify drl=off.

You can also specify vxassist-style storage attributes to define the disks that can or cannot be used for the plexes of the DCO volume.

Note: The vxsnap prepare command automatically enables FastResync on the volume and on any snapshots that are generated from it.

If the volume is a RAID-5 volume, it is converted to a layered volume that can be used with snapshots and FastResync.

Adding traditional DRL logging to a mirrored volume

Note: The procedure described in this section creates a DRL log that is configured within a dedicated DRL plex. The version 20 DCO volume layout includes space for a DRL log. The new DCO volume layout also supports traditional (third-mirror), instant (copy-on-write), and instant space-optimized snapshots. However, a version 20 DCO volume cannot be used in conjunction with a separate DRL plex. For full details, see “Preparing a volume for DRL and instant snapshots” on page 275.

To put dirty region logging (DRL) into effect for a mirrored volume, a log subdisk must be added to that volume. Only one log subdisk can exist per plex.

To add DRL logs to an existing volume, use the following command:

#vxassist [-b] [-g diskgroup] addlog volume logtype=drl \ [nlog=n] [loglen=size]

Note: If specified, the -boption makes adding the new logs a background task.

The nlog attribute can be used to specify the number of log plexes to add. By default, one log plex is added. The loglen attribute specifies the size of the log,