Preparing a volume for DRL and instant snapshots

You can add a version 20 data change object (DCO) and DCO volume to an existing volume if the disk group version number is 110 or greater. You can also simultaneously create a new volume, a DCO and DCO volume, and enable DRL as long as the disk group version is 110 or greater.


You need a license key to use the DRL and FastResync feature. If you do not have a license key, you can configure a DCO object and DCO volume so that snap objects are associated with the original and snapshot volumes. However, without a license key, only full resynchronization can be performed.

To add a version 20 DCO and DCO volume to a volume, use the following command :

# vxsnap [-g diskgroup] prepare volume [ndcomirs=number] \ 
  [regionsize=size] [drl=on|sequential|off] \
  [storage_attribute ...]

The ndcomirs attribute specifies the number of DCO plexes that are created in the DCO volume. You should configure as many DCO plexes as there are data and snapshot plexes in the volume. The DCO plexes are used to set up a DCO volume for any snapshot volume that you subsequently create from the snapshot plexes. For example, specify ndcomirs=5 for a volume with 3 data plexes and 2 snapshot plexes.

The value of the regionsize attribute specifies the size of the tracked regions in the volume. A write to a region is tracked by setting a bit in the change map. The default value is 64k (64KB). A smaller value requires more disk space for the change maps, but the finer granularity provides faster resynchronization.

To enable DRL logging on the volume, specify drl=on (this is the default). For sequential DRL, specify drl=sequential. If you do not need DRL, specify drl=off.

You can also specify vxassist-style storage attributes to define the disks that can or cannot be used for the plexes of the DCO volume.

The vxsnap prepare command automatically enables Persistent FastResync on the volume. Persistent FastResync is also set automatically on any snapshots that are generated from a volume on which this feature is enabled.

If the volume is a RAID-5 volume, it is converted to a layered volume that can be used with instant snapshots and Persistent FastResync.

By default, a version 20 DCO volume contains 32 per-volume maps. If you require more maps, you can use the vxsnap addmap command to add them.

See the vxsnap(1M) manual page.

More Information

Determining the DCO version number

Creating a volume with a version 20 DCO volume

Upgrading existing volumes to use version 20 DCOs

How persistent FastResync works with snapshots

Specifying storage for version 20 DCO plexes

Using a DCO and DCO volume with a RAID-5 volume