Upgrading existing volumes to use version 20 DCOs

You can upgrade a volume created before VxVM 4.0 to take advantage of new features such as instant snapshots and DRL logs that are configured within the DCO volume. You must upgrade the version of the disk groups, remove snapshots and version 0 DCOs that are associated with volumes in the disk groups, and configure the volumes with version 20 DCOs.


The plexes of the DCO volume require persistent storage space on disk to be available. To make room for the DCO plexes, you may need to add extra disks to the disk group, or reconfigure volumes to free up space in the disk group. You can also add disk space by using the disk group move feature to bring in spare disks from a different disk group.

The vxsnap prepare command automatically enables FastResync on the volume and on any snapshots that are generated from it.

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

To upgrade an existing disk group and the volumes that it contains

  1. Upgrade the disk group that contains the volume to the latest version before performing the remainder of the procedure described in this section. To check the version of a disk group, use the following command :

    # vxdg list diskgroup

    To upgrade a disk group to the latest version, use the following command:

    # vxdg upgrade diskgroup

  2. To discover which volumes in the disk group have version 0 DCOs associated with them, use the following command:

    # vxprint [-g diskgroup] -F "%name" -e "v_hasdcolog"

    This command assumes that the volumes can only have version 0 DCOs as the disk group has just been upgraded.

    To upgrade each volume within the disk group, repeat the following steps as required.

  3. If the volume to be upgraded has a traditional DRL plex or subdisk (that is, the DRL logs are not held in a version 20 DCO volume), use the following command to remove this:

    # vxassist [-g diskgroup] remove log volume [nlog=n]

    To specify the number, n, of logs to be removed, use the optional attribute nlog=n . By default, the vxassist command removes one log.

  4. For a volume that has one or more associated snapshot volumes, use the following command to reattach and resynchronize each snapshot:

    # vxassist [-g diskgroup] snapback snapvol

    If FastResync was enabled on the volume before the snapshot was taken, the data in the snapshot plexes is quickly resynchronized from the original volume. If FastResync was not enabled, a full resynchronization is performed.

  5. To turn off FastResync for the volume, use the following command :

    # vxvol [-g diskgroup] set fastresync=off volume
  6. To dissociate a version 0 DCO object, DCO volume and snap objects from the volume, use the following command:

    # vxassist [-g diskgroup] remove log volume logtype=dco
  7. To upgrade the 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 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 you need sequential DRL, specify drl=sequential. If you do not need DRL, specify drl=off.

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

More Information

Reorganizing the contents of disk groups

Upgrading a disk group

Determining the DCO version number