Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 8, Administering Volumes
Preparing a Volume for DRL and Instant Snapshots
235
See “Adding a RAID-5 Log” on page 243 for information on adding RAID-5 logs to a
RAID-5 volume.
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 212. 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 240.
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 53. See “Determining
the DCO Version Number” on page 238 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.