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

374 Administering hot-relocation
How hot-relocation works
home-02
src-02
mkting-01
failing disks:
mydg02
This message shows that mydg02 was detached by a failure. When a disk is detached, I/O
cannot get to that disk. The plexes home-02, src-02, and mkting-01 were also
detached (probably because of the failure of the disk).
As described in “Partial disk failure mail messages” on page 372, the problem can be a
cabling error. If the problem is not a cabling error, replace the disk (see “Removing and
replacing disks” on page 112).
How space is chosen for relocation
A spare disk must be initialized and placed in a disk group as a spare before it can be used
for replacement purposes. If no disks have been designated as spares when a failure
occurs, VxVM automatically uses any available free space in the disk group in which the
failure occurs. If there is not enough spare disk space, a combination of spare space and
free space is used.
The free space used in hot-relocation must not have been excluded from hot-relocation
use. Disks can be excluded from hot-relocation use by using
vxdiskadm, vxedit or the
Veritas Enterprise Administrator (VEA).
You can designate one or more disks as hot-relocation spares within each disk group.
Disks can be designated as spares by using
vxdiskadm, vxedit, or the VEA. Disks
designated as spares do not participate in the free space model and should not have storage
space allocated on them.
When selecting space for relocation, hot-relocation preserves the redundancy
characteristics of the VxVM object to which the relocated subdisk belongs. For example,
hot-relocation ensures that subdisks from a failed plex are not relocated to a disk
containing a mirror of the failed plex. If redundancy cannot be preserved using any
available spare disks and/or free space, hot-relocation does not take place. If relocation is
not possible, the system administrator is notified and no further action is taken.
From the eligible disks, hot-relocation attempts to use the disk that is “closest” to the
failed disk. The value of “closeness” depends on the controller, target, and disk number of
the failed disk. A disk on the same controller as the failed disk is closer than a disk on a
different controller. A disk under the same target as the failed disk is closer than one on a
different target.
Hot-relocation tries to move all subdisks from a failing drive to the same destination disk,
if possible.