Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

# cat /proc/sys/vxvm/vxio/vol_max_volumes
4079
See the vxdg(1M) manual page.
Handling cloned disks with duplicated identifiers
A disk may be copied by creating a hardware snapshot (such as an EMC BCV™ or
Hitachi ShadowCopy™) or clone, by using dd or a similar command to replicate
the disk, or by building a new LUN from the space that was previously used by a
deleted LUN. To avoid the duplicate disk ID condition, the default action of VxVM
is to prevent such duplicated disks from being imported.
Advanced disk arrays provide hardware tools that you can use to create clones of
existing disks outside the control of VxVM. For example, these disks may have
been created as hardware snapshots or mirrors of existing disks in a disk group.
As a result, the VxVM private region is also duplicated on the cloned disk. When
the disk group containing the original disk is subsequently imported, VxVM detects
multiple disks that have the same disk identifier that is defined in the private
region. In releases prior to 5.0, if VxVM could not determine which disk was the
original, it would not import such disks into the disk group. The duplicated disks
would have to be re-initialized before they could be imported.
From release 5.0, a unique disk identifier (UDID) is added to the disk’s private
region when the disk is initialized or when the disk is imported into a disk group
(if this identifier does not already exist). Whenever a disk is brought online, the
current UDID value that is known to the Device Discovery Layer (DDL) is compared
with the UDID that is set in the disk’s private region. If the UDID values do not
match, the udid_mismatch flag is set on the disk. This flag can be viewed with the
vxdisk list command. This allows a LUN snapshot to be imported on the same
host as the original LUN. It also allows multiple snapshots of the same LUN to be
simultaneously imported on a single server, which can be useful for off-host
backup and processing.
A new set of vxdisk and vxdg operations are provided to handle such disks; either
by writing the DDL value of the UDID to a disk’s private region, or by tagging a
disk and specifying that it is a cloned disk to the vxdg import operation.
The following is sample output from the vxdisk list command showing that
disks c2t66d0, c2t67d0 and c2t68d0 are marked with the udid_mismatch flag:
# vxdisk list
DEVICE TYPE DISK GROUP STATUS
c0t06d0 auto:cdsdisk - - online
c0t16d0 auto:cdsdis - - online
Creating and administering disk groups
Handling cloned disks with duplicated identifiers
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