Upgrading Existing Volumes to Use Version 20 DCOs

The procedure described in this section describes how to upgrade a volume created before VxVM 4.0 so that it can take advantage of new features such as instant snapshots, and DRL logs that are configured within the DCO volume. This requires upgrading the version of the disk groups, removing any existing snapshots and version 0 DCOs that are associated with volumes in the disk groups, and finally configuring the volumes with version 20 DCOs.

Perform the following steps 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. Use the following command to check the version of a disk group:
   # vxdg list diskgroup

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

   
   # vxdg upgrade diskgroup

   For more information, see Upgrading a Disk Group.

2. Use the following command to discover which volumes in the disk group have version 0 DCOs associated with them:
   # vxprint [-g diskgroup] -F "%name" -e "v_hasdcolog"

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     Note    This command assumes that the volumes can only have version 0 DCOs as the disk group has just been upgraded. See Determining the DCO Version Number for a description of how to find out the DCO version number of a volume in any disk group.

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3. Repeat the following steps to upgrade each volume within the disk group as required:
   1. 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]

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

   2. 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.

   3. Use the following command to turn off FastResync for the volume:
   
      # vxvol [-g diskgroup] set fastresync=off volume
   4. Use the following command to dissociate a version 0 DCO object, DCO volume and snap objects from the volume:
   
      # vxassist [-g diskgroup] remove log volume logtype=dco
   5. Use the following command on the volume to upgrade it:
   
       # 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 or cannot be used for the plexes of the DCO volume.

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     Note    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.

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