Filter
Top Products
321Administering volume snapshots
Creating instant snapshots
Preparing to create instant and break-off snapshots
To prepare a volume for the creation of instant and break-off snapshots
1 Use the following commands to see if the volume is associated with a
version 20 data change object (DCO) and DCO volume that allow instant
snapshots and Persistent FastResync to be used with the volume, and to
check that FastResync is enabled on the volume:
# vxprint -g volumedg -F%instant volume
# vxprint -g volumedg -F%fastresync volume
If both commands return a value of on, the volume can be used for instant
snapshot operations, and you should skip to step 3. Otherwise continue
with step 2.
2 To prepare a volume for instant snapshots, use the following command:
# vxsnap [-g diskgroup] prepare volume [regionsize=size] \
[ndcomirs=number] [alloc=storage_attributes]
Note: It is only necessary to run the vxsnap prepare command on a volume
if it does not already have a version 20 DCO volume (for example, if you
have run the
vxsnap unprepare command on the volume). See “Creating a
volume with a version 20 DCO volume” on page 252, “Preparing a volume
for DRL and instant snapshots” on page 275 and “Removing support for
DRL and instant snapshots from a volume” on page 279 for more
information.
For example, to prepare the volume, myvol, in the disk group, mydg, use
the following command:
# vxsnap -g mydg prepare myvol regionsize=128k ndcomirs=2 \
alloc=mydg10,mydg11
This example creates a DCO object and redundant DCO volume with two
plexes located on disks mydg10 and mydg11, 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.
3 If you need to create several space-optimized instant snapshots for the
volumes in a disk group, you may find it more convenient to create a single
shared cache object in the disk group rather than a separate cache object for
each snapshot. Follow the procedure in “Creating a shared cache object” on
page 322 to create the cache object.
For full-sized instant snapshots and linked break-off snapshots, you must
prepare a volume that is to be used as the snapshot volume. This volume
must be the same size as the data volume for which the snapshot is being