VERITAS Storage Foundation 4.1 Intelligent Storage Provisioning Administrator's Guide

Chapter 5, Administering Instant Snapshots
Creating Instant Snapshots
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This example creates a DCO object and redundant DCO volume with two plexes, 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.
Note If you intend to create space-optimized instant snapshots that share a cache volume, the
region size that you specify for the volume must be greater than or equal to any region
size that you specify for the cache volume. Creation of space-optimized snapshots that
use a shared cache fails if the region size of the volume is smaller than the region size of
the cache.
If the region size of a space-optimized snapshot differs from the region size of the
cache, this can degrade the system’s performance compared to the case where the region
sizes are the same.
3. Use the vxsnap make step to create an instant snapshot that is immediately available for
making a backup. If you specify a name or size for a storage cache, a space-optimized snapshot
is created that requires less space than does a full-sized instant snapshot volume.
❖ To create a full-sized instant snapshot, snapvol, use one of the following forms of the vxsnap
make command:
# vxsnap [-g diskgroup] make source=volume/snapvol=snapvol\
[/syncing=off]
Note The attributes for a snapshot are specified as a tuple. The vxsnap make command
accepts multiple tuples; one for each snapshot that is being created. A tuple for a
full-sized instant snapshot must contain a source attribute and a snapvol attribute.
Each element of a tuple is separated from the next by a slash character (/). Tuples are
separated by white space.
This command specifies an existing volume, snapvol, that is to be used as the snapshot
volume. See “Creating a Volume for Use as a Full-Sized Instant Snapshot” on page 76 for
details.
Background synchronization of the snapshot volume from its parent volume is enabled by
default (equivalent to specifying the syncing=on attribute). If you do not want to move the
snapshot into a separate disk group, or turn it into an independent volume, specify the
syncing=off attribute to disable synchronization. This avoids unnecessary system
overhead.
For example, to use the prepared volume, snap1myvol, as the snapshot for the volume,
myvol, in the disk group, mydg, use the following command:
# vxsnap -g mydg make source=myvol/snapvol=snap1myvol