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Preparing a volume for DRL and instant snapshots

You can add a version 20 data change object (DCO) and DCO volume to a volume that you previously created in a disk group with a version number of 110 or greater. If you are creating a new volume in a disk group with a version number of 110 or greater, you can create the DCO and DCO volume and enable DRL at the same time as you create the volume.

See "Determining the DCO version number" on page 288.

See "Creating a volume with a version 20 DCO volume" on page 261.

See "Upgrading existing volumes to use version 20 DCOs" on page 289.

  Note   You need a license to use the DRL and FastResync feature. If you do not have a license, 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, only full resynchronization can be performed.

See "How persistent FastResync works with snapshots" on page 72.

Use the following command to add a version 20 DCO and DCO volume to a volume:

# 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. It is recommended that you 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 setting). If sequential DRL is required, specify drl=sequential. If DRL is not required, specify drl=off.

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

See "Specifying storage for version 20 DCO plexes" on page 286.

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.

See "Using a DCO and DCO volume with a RAID-5 volume" on page 287.

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

See the vxsnap(1M) manual page.