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275Administering volumes
Preparing a volume for DRL and instant snapshots
Preparing a volume for DRL and instant snapshots
Note: This procedure describes how to add a version 20 data change object (DCO)
and DCO volume to a volume that you previously created in a disk group with a
version number of 110 or greater. If you are creating a new volume in a disk
group with a version number of 110 or greater, you can specify the co-creation
of a DCO and DCO volume and enable DRL as described in “Creating a volume
with a version 20 DCO volume” on page 252. If the volume was created in a
release prior to VxVM 4.0, use the procedure in “Upgrading existing volumes to
use version 20 DCOs” on page 279.
You need a full VxVM license and a Veritas FlashSnap
TM
or FastResync license to
use the DRL and FastResync features. Even if you do not have a license, you can
configure a DCO object and DCO volume so that snap objects are associated with
the original and snapshot volumes. For more information about snap objects,
see “How persistent FastResync works with snapshots” on page 70. See
“Determining the DCO version number” on page 277 for details of how to
determine the version number of a volume’s DCO.
Use the following command to add a version 20 DCO and DCO volume to a
volume:
# 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 storage attributes to define the disks that can and/or
cannot be used for the plexes of the DCO volume. See “Specifying storage for
version 20 DCO plexes” on page 276 for details.