Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

315Administering volume snapshots
Creating instant snapshots
Creating and managing space-optimized instant snapshots
Note: Space-optimized instant snapshots are not suitable for write-intensive volumes
(such as for database redo logs) because the copy-on-write mechanism may degrade the
performance of the volume.
If you intend to split the volume and snapshot into separate disk groups (for example, to
perform off-host processing), you must use a fully synchronized full-sized instant, third-
mirror break-off or linked break-off snapshot (which do not require a cache object). You
cannot use a space-optimized instant snapshot for this purpose.
Creation of space-optimized snapshots that use a shared cache fails if the region size
specified for the volume is smaller than the region size set on 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.
For space-optimized instant snapshots that share a cache object, the specified region size
must be greater than or equal to the region size specified for the cache object. See
“Creating a shared cache object” on page 312 for details.
The attributes for a snapshot are specified as a tuple to the
vxsnap make command. This
command accepts multiple tuples. One tuple is required for each snapshot that is being
created. Each element of a tuple is separated from the next by a slash character (/). Tuples
are separated by white space.
To create and manage a space-optimized instant snapshot
1Use the
vxsnap make command to create a space-optimized instant snapshot. This
snapshot can be created by using an existing cache object in the disk group, or a new
cache object can be created for its use.
◆ To create a space-optimized instant snapshot, snapvol, that uses a named shared
cache object:
# vxsnap [-g diskgroup] make source=vol/newvol=snapvol\
/[cache=cacheobject] [alloc=storage_attributes]
For example, to create the space-optimized instant snapshot, snap3myvol, of the
volume, myvol, in the disk group, mydg, on the disk mydg14, and which uses the
shared cache object, cobjmydg, use the following command:
# vxsnap -g mydg make source=myvol/newvol=snap3myvol\
/cache=cobjmydg alloc=mydg14
For details of how to create a shared cache object, see “Creating a shared cache
object” on page 312.