Veritas Storage Foundation 5.1 SP1 Advanced Features Administrator"s Guide (5900-1503, April 2011)
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 215.
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
The DCO is created on the specified allocation.
■ To create a space-optimized instant snapshot, snapvol, and also create a
cache object for it to use:
# vxsnap [-g diskgroup] make source=vol/newvol=snapvol\
[/cachesize=size][/autogrow=yes][/ncachemirror=number]\
[alloc=storage_attributes]
The cachesize attribute determines the size of the cache relative to the
size of the volume. The autogrow attribute determines whether VxVM
will automatically enlarge the cache if it is in danger of overflowing. By
default, autogrow=on and the cache is automatically grown.
If autogrow is enabled, but the cache cannot be grown, VxVM disables the
oldest and largest snapshot that is using the same cache, and releases its
cache space for use.
219Administering volume snapshots
Creating instant snapshots