Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009
Creating and managing space-optimized instant snapshots
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
performance.
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.
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.
See “Creating a shared cache object” on page 368.
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
1
Use 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.
■ 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
See “Creating a shared cache object” on page 368.
■ To create a space-optimized instant snapshot, snapvol, and also create a
cache object for it to use:
371Administering volume snapshots
Creating instant snapshots