Veritas Storage Foundation Intelligent Storage Provisioning 5.0 AdministratorÆs Guide, HP-UX 11i v3, First Edition, May 2008

103Administering instant snapshots
Creating instant snapshots
Preparing to create instant and break-off snapshots
To prepare a volume for the creation of instant and break-off snapshots
1 Use the following commands to see if the volume is associated with a
version 20 data change object (DCO) and DCO volume that allow instant
snapshots and Persistent FastResync to be used with the volume, and to
check that FastResync is enabled on the volume:
# vxprint -g volumedg -F%instant volume
# vxprint -g volumedg -F%fastresync volume
If both commands return a value of on, the volume can be used for instant
snapshot operations, and you should skip to step 3. Otherwise continue
with step 2.
2 To prepare a volume for instant snapshots, use the following command:
# vxsnap [-g diskgroup ] prepare volume [regionsize= size ] \
[ndcomirs=
number ] [alloc= storage_attributes ]
For example, to prepare the volume, myvol, in the disk group, mydg, use the
following command:
# vxsnap -g mydg prepare myvol regionsize=128k ndcomirs=2 \
alloc=mydg10,mydg11
This example creates a DCO object and redundant DCO volume with two
plexes located on disks mydg10 and mydg11, and associates them with
myvol. The region size is also increased to 128KB from the default size of
64KB. The region size must be a power of 2, and be greater than or equal to
16KB. A smaller value requires more disk space for the change maps, but
the finer granularity provides faster resynchronization.
3 If you intend to take a space-optimized instant snapshot of the volume, you
must first set up a shared cache volume in the same disk group as the
volume. This cache object for this cache volume can be maintained by using
the
vxcache command.
For full-sized instant snapshots, linked break-off snapshots and space-
optimized instant snapshots, you must also create a volume for use as the
snapshot volume. This volume must have the same region size as that of the
volume for which the snapshot is being created. In addition, a volume that
is created for use as a full-sized instant snapshot must be the same size as
the volume for which the snapshot is being created.
See “Creating a shared cache volume and preparing space-optimized
snapshots” on page 97.
See “Creating a volume for use as a full-sized instant or linked break-off
snapshot” on page 96.