Creating a Volume with a Version 0 DCO Volume

If a data change object (DCO) and DCO volume are associated with a volume, this allows Persistent FastResync to be used with the volume. (See How Persistent FastResync Works with Snapshots for details of how Persistent FastResync performs fast resynchronization of snapshot mirrors when they are returned to their original volume.)

To perform fast resynchronization of mirrors after a system crash or reboot, you must also enable dirty region logging (DRL) on a mirrored volume. To add a DCO object and DCO volume to a volume on which DRL logging is enabled, follow the procedure described in Adding a Version 0 DCO and DCO Volume.

To create a volume with an attached version 0 DCO object and volume, use the following procedure:

1. Ensure that the disk group has been upgraded to version 90. Use the following command to check the version of a disk group:
   # vxdg list diskgroup

   To upgrade a disk group to version 90, use the following command:

   
   # vxdg -T 90 upgrade diskgroup

   For more information, see Upgrading a Disk Group.

2. Use the following command to create the volume (you may need to specify additional attributes to create a volume with the desired characteristics):
   # vxassist [-g diskgroup] make volume length layout=layout \
     logtype=dco [ndcomirror=number] [dcolen=size] [fastresync=on] \
     [other attributes]

   For non-layered volumes, the default number of plexes in the mirrored DCO volume is equal to the lesser of the number of plexes in the data volume or 2. For layered volumes, the default number of DCO plexes is always 2. If required, use the ndcomirror attribute to specify a different number. It is recommended that you configure as many DCO plexes as there are data plexes in the volume. For example, specify ndcomirror=3 when creating a 3-way mirrored volume.

   The default size of each plex is 132 blocks unless you use the dcolen attribute to specify a different size. If specified, the size of the plex must be a multiple of 33 blocks from 33 up to a maximum of 2112 blocks.

   By default, FastResync is not enabled on newly created volumes. Specify the fastresync=on attribute if you want to enable FastResync on the volume. If a DCO object and DCO volume are associated with the volume, Persistent FastResync is enabled; otherwise, Non-Persistent FastResync is enabled.

3. To enable DRL or sequential DRL logging on the newly created volume, use the following command:
   # vxvol [-g diskgroup] set logtype=drl|drlseq volume

For more information, see the vxassist(1M) and vxvol(1M) manual pages.

If you use ordered allocation when creating a mirrored volume on specified storage, you can use the optional logdisk attribute to specify on which disks dedicated log plexes should be created. Use the following form of the vxassist command to specify the disks from which space for the logs is to be allocated:

If you do not specify the logdisk attribute, vxassist locates the logs in the data plexes of the volume.

For more information about ordered allocation, see Specifying Ordered Allocation of Storage to Volumes and the vxassist(1M) manual page.