Administering volume snapshots 325

Creating instant snapshots

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 322 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 322.

◆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, the cache is not grown.

Note: 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.

The ncachemirror attribute specifies the number of mirrors to create in the cache volume. For backup purposes, the default value of 1 should be sufficient.