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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.)

  Note   The procedure described in this section creates a volume with a data change object (DCO) and DCO volume that has a version 0 layout as introduced in VxVM 3.2. The version 0 layout supports traditional (third-mirror) snapshots, but not full-sized instant snapshots, space-optimized instant snapshots nor DRL configured within the DCO volume. See Version 0 DCO volume layout and Version 20 DCO volume layout for a description of the differences between the old and new DCO volume layouts.

For details of how to configure a volume with a version 20 DCO and DCO volume, see Creating a volume with a version 20 DCO volume. This is the preferred and recommended method.

See Determining the DCO version number for details of how to determine the version number of a volume's DCO.

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.

  Note   You need a Veritas FlashSnap^TM or FastResync license to use the Persistent FastResync feature. Even 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. For more information about snap objects, see How persistent FastResync works with snapshots.

 To create a volume with an attached version 0 DCO object and volume

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:

# vxassist [-g diskgroup] -o ordered make volume length \

  layout=mirror logtype=log_type logdisk=disk[,disk,...] \

  storage_attributes

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.