VERITAS Storage Foundation 4.1 Intelligent Storage Provisioning Administrator's Guide

Creating Instant Snapshots
82 VERITAS Storage Foundation ISP Administrator’s Guide
To back up a volume with the vxsnap command, use the following procedure:
1. 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 both full-sized 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 77
for details of how to set up a shared cache volume, and how to prepare space-optimized
snapshots that share this cache.
See “Creating a Volume for Use as a Full-Sized Instant Snapshot” on page 76 for details of
how to prepare a volume for use as a full-sized instant snapshot.
Note If you intend to split the clone pool that contains snapshots into separate disk groups
(for example, to perform off-host processing), the clone pool must only contain fully
synchronized full-sized instant snapshots (which do not require a cache volume). You
cannot split off a clone pool that contains either a cache volume or space-optimized
instant snapshots.
2. Use the following commands on the primary host 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 these command return a value of on, the volume can be used for instant snapshot
operations.
To prepare a volume for instant snapshots, use the following command:
# vxsnap [-g diskgroup] prepare volume [regionsize=size] \
[ndcomirs=number] [alloc=storage_attributes]
Note It is only necessary to run this command on a volume if it does not already have a
version 20 DCO volume.
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