VxVM has detected disks with duplicate disk identifiers. Arrays with mirroring capability in hardware are particularly susceptible to such data corruption, but other causes are possible as explained below.
In releases prior to 3.5, VxVM selected the first disk that it found if the selection process failed. From release 3.5, the default behavior of VxVM was to avoid the selection of the wrong disk as this could lead to data corruption.
If VxVM could not determine which disk was the original, it would not import the disks until they were reinitialized with a new disk ID.
From release 5.0, VxVM checks the unique disk identifier (UDID) value that is known to the Device Discovery Layer (DDL) against the UDID value that is set in the disk's private region. The
udid_mismatch flag is set on the disk if the values differ. If set, this flag is displayed in the output from the
vxdisk list command.
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.
User intervention is required in the following cases:
- Case 1: Some arrays such as EMC and HDS provide mirroring in hardware. When a LUN pair is split, depending on how the process is performed, this can result in two disks that have the same disk identifier and UDID value. See "Handling Disks with Duplicated Identifiers" in the "Creating and Administering Disk Groups" chapter of the Veritas Volume Manager Administrator's Guide for full details of how to deal with this condition.
- Case 2: If disks have been duplicated by using the dd command or any similar copying utility, you can use the following command to update the UDID for one or more disks:
# vxdisk [-f] updateudid disk1 ...
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 set the udid_mismatch flag on a disk.
For example, the following command updates the UDIDs for the disks c2t66d0 and c2t67d0:
# vxdisk updateudid c2t66d0 c2t67d0
- Case 3: If DMP has been disabled to an array that has multiple paths, then each path to the array is claimed as a unique disk.
If DMP is suppressed, VxVM does not know which path to select as the true path. You must choose which path to use. Decide which path to exclude, and then select item 1 (suppress all paths through a controller from VxVM's view) or item 2 (suppress a path from VxVM's view) from vxdiskadm option 17 (Prevent multipathing/Suppress devices from VxVM's view).
If only one array is connected to the controller, suppress the path from DMP using item 5 (Prevent multipathing of all disks on a controller by VxVM), and then item 1 (Suppress all paths through a controller from VxVM's view), from vxdiskadm option 17 (Prevent multipathing/Suppress devices from VxVM's view).
If more than one array is connected to the controller, suppress the path from DMP using item 5 (Prevent multipathing of all disks on a controller by VxVM), and then item 2 (Suppress a path from VxVM's view), from vxdiskadm option 17 (Prevent multipathing/Suppress devices from VxVM's view).
