Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

See “Adding a RAID-5 log” on page 382.
Preparing a volume for DRL and instant snapshots
You can add a version 20 data change object (DCO) and DCO volume to an existing
volume if the disk group version number is 110 or greater. You can also
simultaneously create a new volume, a DCO and DCO volume, and enable DRL as
long as the disk group version is 110 or greater.
See “Determining the DCO version number” on page 362.
See “Creating a volume with a version 20 DCO volume” on page 316.
See “Upgrading existing volumes to use version 20 DCOs” on page 366.
Note: You need a license key to use the DRL and FastResync feature. If you do not
have a license key, you can configure a DCO object and DCO volume so that snap
objects are associated with the original and snapshot volumes. However, without
a license key, only full resynchronization can be performed.
See “How persistent FastResync works with snapshots” on page 67.
To add a version 20 DCO and DCO volume to a volume, use the following command
:
# vxsnap [-g diskgroup] prepare volume [ndcomirs=number] \
[regionsize=size] [drl=on|sequential|off] \
[storage_attribute ...]
The ndcomirs attribute specifies the number of DCO plexes that are created in
the DCO volume. You should configure as many DCO plexes as there are data and
snapshot plexes in the volume. The DCO plexes are used to set up a DCO volume
for any snapshot volume that you 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). For
sequential DRL, specify drl=sequential. If you do not need DRL, 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.
359Administering volumes
Preparing a volume for DRL and instant snapshots