Adding an instant snap DCO and DCO volume

To prepare a volume for instant snapshots, an instant snap data change object (DCO) and DCO volume must be associated with that volume. This procedure also enables Persistent FastResync on the volume.

The following procedure is required only if the volume does not have an instant snap DCO volume.

By default, volumes on thin provisioning LUNs are created with an instant snap DCO volume.

To add an instant snap DCO and DCO volume

  1. Verify that the volume has an instant snap data change object (DCO) and DCO volume, and 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, 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]

    Run the vxsnap prepare command on a volume only if it does not have an instant snap DCO volume.

    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 several space-optimized instant snapshots for the volumes in a disk group, you may find it convenient to create a single shared cache object in the disk group rather than a separate cache object for each snapshot.

    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 created, and it must also have the same region size.

More Information

Creating a shared cache object

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