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277Administering volumes
Preparing a volume for DRL and instant snapshots
If required, you can use the vxassist move command to relocate DCO plexes to
different disks. For example, the following command moves the plexes of the
DCO volume, vol1_dcl, for volume vol1 from disk03 and disk04 to disk07
and disk08:
# vxassist -g mydg move vol1_dcl !disk03 !disk04 disk07 disk08
For more information, see “Moving DCO volumes between disk groups” on
page 200, and the
vxassist(1M) and vxsnap(1M) manual pages.
Using a DCO and DCO volume with a RAID-5 volume
The procedure in the previous section can be used to add a DCO and DCO volume
to a RAID-5 volume. This allows you to use Persistent FastResync on the volume
for fast resynchronization of snapshots on returning them to their original
volume. However, the procedure has the side effect of converting the RAID-5
volume into a special type of layered volume. You can create space-optimized
instant snapshots of such a volume, and you can add mirrors that may be broken
off as full-sized instant snapshots. You cannot relayout or resize such a volume
unless you convert it back to a pure RAID-5 volume.
To convert a volume back to a RAID-5 volume, remove any snapshot plexes from
the volume, and dissociate the DCO and DCO volume from the layered volume
using the procedure described in “Removing support for DRL and instant
snapshots from a volume” on page 279. You can then perform relayout and
resize operations on the resulting non-layered RAID-5 volume.
To allow Persistent FastResync to be used with the RAID-5 volume again, re-
associate the DCO and DCO volume as described in “Preparing a volume for DRL
and instant snapshots” on page 275.
Note: Dissociating a DCO and DCO volume disables FastResync on the volume. A
full resynchronization of any remaining snapshots is required when they are
snapped back.
Determining the DCO version number
The instant snapshot and DRL-enabled DCO features require that a version 20
DCO be associated with a volume, rather than an earlier version 0 DCO.
To find out the version number of a DCO that is associated with a volume
1 Use the
vxprint command on the volume to discover the name of its DCO:
# DCONAME=‘vxprint [-g diskgroup] -F%dco_name volume‘
2 Use the vxprint command on the DCO to determine its version number:
# vxprint [-g diskgroup] -F%version $DCONAME