< Previous  | TOC | Index | Next  >

Preparing to create instant and break-off snapshots

Prepare a volume for the creation of 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]

   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 intend to take a space-optimized instant snapshot of the volume, you must first set up a shared cache volume in the same disk group as the volume. This cache object for this cache volume can be maintained by using the vxcache command.

   For full-sized instant snapshots, linked break-off snapshots and space-optimized instant snapshots, you must also create a volume for use as the snapshot volume. This volume must have the same region size as that of the volume for which the snapshot is being created. In addition, a volume that is created for use as a full-sized instant snapshot must be the same size as the volume for which the snapshot is being created.

   See Creating a shared cache volume and preparing space-optimized snapshots.

   See Creating a volume for use as a full-sized instant or linked break-off snapshot.

   If you intend to split the clone pool that contains snapshots into separate disk groups (for example, to perform off-host processing), the clone pool must only contain fully synchronized full-sized instant snapshots (which do not require a cache volume). You cannot split off a clone pool that contains either a cache volume or space-optimized instant snapshots.