Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

190 Creating and administering disk groups
Reorganizing the contents of disk groups
Listing objects potentially affected by a move
To display the VxVM objects that would be moved for a specified list of objects, use the
following command:
# vxdg [-o expand] listmove sourcedg targetdg object ...
The following example lists the objects that would be affected by moving volume vol1
from disk group mydg to newdg:
# vxdg listmove mydg newdg vol1
mydg01 c0t1d0 mydg05 c1t96d0 vol1 vol1-01 vol1-02 mydg01-01
mydg05-01
However, the following command produces an error because only a part of the volume
vol1 is configured on the disk mydg01:
# vxdg listmove mydg newdg mydg01
VxVM vxdg ERROR V-5-2-4597 vxdg listmove mydg newdg failed
VxVM vxdg ERROR V-5-2-3091 mydg05 : Disk not moving, but
subdisks on it are
Specifying the -o expand option, as shown below, ensures that the list of objects to be
moved includes the other disks (in this case, mydg05) that are configured in vol1:
# vxdg -o expand listmove mydg newdg mydg01
mydg01 c0t1d0 mydg05 c1t96d0 vol1 vol1-01 vol1-02 mydg01-01
mydg05-01
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.
Figure 4-7 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 349 and “Specifying storage for version 20 DCO plexes” on page 268.