Veritas FlashSnap Point-In-Time Copy Solutions 5.0 AdministratorÆs Guide, HP-UX 11i v3, First Edition, May 2008

25Setting up volumes for instant snapshots
Preparing a volume for instant snapshot operations
output for the volume named zoo (the TUTIL0 and PUTIL0 columns are omitted
for clarity):
TY NAME ASSOC KSTATE LENGTH PLOFFS STATE
...
v zoo fsgen ENABLED 1024 - ACTIVE
pl zoo-01 zoo ENABLED 1024 - ACTIVE
sd disk01-01 zoo-01 ENABLED 1024 0 -
pl foo-02 zoo ENABLED 1024 - ACTIVE
sd disk02-01 zoo-02 ENABLED 1024 0 -
dc zoo_dco zoo - - - -
v zoo_dcl gen ENABLED 132 - ACTIVE
pl zoo_dcl-01 zoo_dcl ENABLED 132 - ACTIVE
sd disk03-01 zoo_dcl-01 ENABLED 132 0 -
pl zoo_dcl-02 zoo_dcl ENABLED 132 - ACTIVE
sd disk 04-01 zoo_dcl-02 ENABLED 132 0 -
In this output, the DCO object is shown as zoo_dco, and the DCO volume as
zoo_dcl with 2 plexes, zoo_dcl-01 and zoo_dcl-02.
For more information, see “Considerations for placing DCO plexes” on page 25,
and the
vxassist(1M) and vxsnap(1M) manual pages.
Considerations for placing DCO plexes
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 the version 20 DCOs in
VxVM 4.0 and later releases 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 I/O performance of the volume, and provides
resilience for the DRL logs.
If you use the
vxsnap prepare command to set up a DCO, you must ensure that
the disks that contain the plexes of the DCO volume accompany their parent
volume during the move. Use the
vxprint command on a volume to examine the
configuration of its associated DCO volume.
Figure 2-1 illustrates some instances in which it is not be possible to split a disk
group because of the location of the DCO plexes.
For more information about relocating DCO plexes, see “Preparing a volume for
instant snapshot operations” on page 23.