Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

272 Administering volumes
Adding traditional DRL logging to a mirrored volume
6 Use the following command to dissociate a version 0 DCO object, DCO volume and
snap objects from the volume:
# vxassist [-g diskgroup] remove log volume logtype=dco
7 Use the following command on the volume to upgrade it:
# 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. It is recommended that you 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 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 266.
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.