Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 4, Creating and Administering Disk Groups
Reorganizing the Contents of Disk Groups
161
Moving DCO Volumes Between Disk Groups
When you move the parent volume (such as a snapshot volume) to a different disk group,
its DCO volume must accompany it. If you use the vxassist addlog, vxmake or vxdco
commands to set up a DCO for a volume, you must ensure that the disks that contain the
plexes of the DCO volume accompany their parent volume during the move. You can use
the vxprint command on a volume to examine the configuration of its associated DCO
volume.
If you use the vxassist command or the VERITAS Enterprise Administrator (VEA) to
create both a volume and its DCO, or the vxsnap prepare command to add a DCO to a
volume, the DCO plexes are automatically placed on different disks from the data plexes
of the parent volume. In previous releases, version 0 DCO plexes were placed on the same
disks as the data plexes for convenience when performing disk group split and move
operations. As version 20 DCOs support dirty region logging (DRL) in addition to
Persistent FastResync, it is preferable for the DCO plexes to be separated from the data
plexes. This improves the performance of I/O from/to the volume, and provides
resilience for the DRL logs.
“Examples of Disk Groups That Can and Cannot be Split” on page 162 illustrates some
instances in which it is not be possible to split a disk group because of the location of the
DCO plexes on the disks of the disk group. For more information about relocating DCO
plexes, see “Specifying Storage for Version 0 DCO Plexes” on page 308 and “Specifying
Storage for Version 20 DCO Plexes” on page 236.
For more information about the layout of DCO volumes and their use with volume
snapshots, see and “FastResync” on page 49. For more information about the
administration of volume snapshots, see “Vo lume Sna psh ots” on page 45 and
“Administering Volume Snapshots” on page 261.