Veritas Volume Manager (VxVM) uses a unique disk identifier (UDID) to detect hardware copies of the VxVM disks. Before using a physical volume, VxVM always verifies whether the disk already has a UDID and whether that UDID matches the expected value.

When you initialize a VxVM disk, the Device Discovery Layer (DDL) of VxVM determines the UDID from hardware attributes such as the vendor ID (vid), the product ID (pid), the cabinet serial number, and the LUN serial number. VxVM stores the UDID in the private region of the disk when VxVM first sees a disk that does not have a UDID, or when VxVM initializes the disk. The exact make-up of the UDID depends on the array storage library (ASL). Future versions of VxVM may use different formats for new arrays.

When VxVM discovers a disk with a UDID, VxVM compares the current UDID value (the value determined from the hardware attributes) to the UDID that is already stored on the disk. If the UDID values do not match between the UDID value determined by the DDL and the on-disk UDID, VxVM sets the udid_mismatch flag for the disk.

The udid_mismatch flag generally indicates that the disk is a hardware copy of a VxVM disk. The hardware copy has a copy of the VxVM private region of the original disk, including the UDID. The UDID already stored in the VxVM private region matches the attributes of the original hardware disk, but does not match the value on the hardware disk that is the copy.

With the UDID matching feature, VxVM can prevent the situation where the inconsistent set of disks is presented to the host. This functionality enables you to import a disk group composed of LUN snapshots on the same host as the original LUNs. When you import the disks identified with the udid_mismatch flag, VxVM sets the clone_disk flag on the disk. With care, multiple hardware images of the original LUN can be simultaneously managed and imported on the same host as the original LUN.

See Importing a disk group containing hardware cloned disks .

If a system only sees the copy (or clone) devices, you can remove the clone_disk flags. Only remove the clone_disk flags if you are sure there is no risk. For example, you must make sure that there are not two physical volumes that are copies of the same base physical volume at different times.

If the udid_mismatch flag is set incorrectly on a disk that is not a clone disk, you can remove the udid_mismatch flag and treat the disk as a standard disk.

See the Veritas InfoScale Troubleshooting Guide.