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

167Creating and administering disk groups
Handling disks with duplicated identifiers
Handling disks with duplicated identifiers
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.
A new set of
vxdisk and vxdg operations are provided to handle such disks; either by
either 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:cdsdisk - - online
...
c2t64d0 auto:cdsdisk - - online
c2t65d0 auto:cdsdisk - - online
c2t66d0 auto:cdsdisk - - online udid_mismatch
c2t67d0 auto:cdsdisk - - online udid_mismatch
c2t68d0 auto:cdsdisk - - online udid_mismatch
Writing a new UDID to a disk
You can use the following command to update the unique disk identifier (UDID) for one
or more disks:
# vxdisk [-f] [-g diskgroup] updateudid disk ...
This command uses the current value of the UDID that is stored in the Device Discovery
Layer (DDL) database to correct the value in the private region. The
-f option must be
specified if VxVM has not raised the udid_mismatch flag for a disk.
For example, the following command updates the UDIDs for the disks c2t66d0 and
c2t67d0: