Description

UDID (Unique Disk Identifier)

Veritas Volume Manager (VxVM) refers to two UDID values, the UDID value returned by the DDL (Device Discovery Layer) which is the correct (true) UDID value of the LUN, whereas the UDID written on-disk can be from a different source.
 

The UDID structure consists of the Vendor ID (VID), Product ID (PID), Cabinet Serial Number (Cab_Serial_No) and Lun Serial Number (Lun_Serial_No - LSN) :

"VID , '_', PID , '_', CAB _Serial_No , '_', Lun_Serial_No "

Since the writing of this article, the VxVM product has been enhanced and the more recent product versions offer the new vxdisk -px  LIST_* interface

# vxdisk -px LIST_UDID list

DEVICE              UDID                                                                 PRIV_UDID
emc_clariion0_92    DGC%5FVRAID%5FCKM00153100195%5F60060160A0C03D00F07BADEB3BCCEA11      DGC%5FVRAID%5FCKM00153100195%5F60060160A0C03D00F07BADEB3BCCEA11
emc_clariion0_93    DGC%5FVRAID%5FCKM00153100195%5F60060160A0C03D00F27BADEB3BCCEA11      DGC%5FVRAID%5FCKM00153100195%5F60060160A0C03D00F27BADEB3BCCEA11
emc_clariion0_94    DGC%5FVRAID%5FCKM00153100195%5F60060160A0C03D00F47BADEB3BCCEA11      DGC%5FVRAID%5FCKM00153100195%5F60060160A0C03D00F47BADEB3BCCEA11

Other VxVM views also exist, vxdisk -px LIST

Supported Attribute Lists :
 LIST_OFFSET           LIST_CLONE            LIST_DMP
 LIST_UDID             OLD_UDID              LIST_DISK
 LIST_DEVICE           LIST_STATE            CONN_TYPE

Figure 1.0

Lunclasses





Summary:


- Standard (std) disks would normally not report a UDID mismatch state, as the two UDID values would be aligned (match each other).

- Clone (EMC BCV,Symclone, HDS Shadowimage) devices would normally report a UDID mismatch condition, as the clone will inherit the on-disk UDID from the corresponding source disk.

- Replicated (secondary) devices (EMC SRDF/HDS TrueCopy) will report a UDID mismatch condition, as the secondary target disk will inherit the on-disk UDID from the corresponding source (primary) disk.

- False (fake) udid_mismatch can also occur when the UDID structure changes from one VxVM version to another, i.e. when the LUN_SERIAL_NO (LSN) changes in length.
 

Example:

With VxVM 5.1 onwards Veritas changed the lookup location of the LUN_SERIAL_NO (LSN) for EMC related luns. As a result, the EMC LSN is shortened to align with the EMC LSN reported by the EMC syminq interface. Thus, customers upgrading from a Pre-VxVM 5.1 release will encounter a change in the UDID structure for disks initialized before VxVM 5.1. This in turn triggers a udid_mismatch between the VxVM versions.

The UDID related content can be reported using the following vxudidlist.sh script:

Script: vxudidlist.sh

#!/bin/ksh

# vxudidlist.sh - Compare UDID values until upgrading to 6.x which has the "vxdisk -o udid list" command

echo "Check excludes disks reported in online invalid|error|LVM|ZFS states"
echo "DA_NAME DGNAME DDL_UID          PRIV_UDID   CHECK"

for disk in `vxdisk -q list | egrep -v 'online invalid|error|LVM|ZFS' | awk '{ print $1 }'`
do
content=`vxdisk -v list $disk |egrep '(Device|group|udid)' |awk '{ print $2 }' |sed "s/name=/dgname:/g" |sed "s/udid_asl=//g" |tr -s "\n" " "`
echo "$content" | awk '{ if ($3==$4) print $0,"match" ; else print $0,"mismatch" }'
done

# END OF SCRIPT - S.N.Dummer - Jan 2013

The Veritas Volume Manager (VxVM) managed device content (such as the diskid,dgid and on-disk UDID) is cloned/replicated from the source (primary) to the target (secondary) clone/replicated device. This results in an intentional udid_mismatch state on the target clone/replicated devices.

The vxudidlist.sh script enables the user to display UDID related content and displays a "match" or "mismatch" state.

Figure 2.0

The below example highlights an intended udid_mismatch scenario for EMC SRDF replicated devices.
 

The Primary server hosts the SRDF-R1 devices and the Secondary server hosts the SRDF-R2 devices. The on-disk UDID content is then replicated from the Primary SRDF-R1 devices to the corresponding SRDF-R2 devices on the Secondary server.

Primary (source) server: 

# vxdisk - eo alldgs list | grep srdf
emc1_0073     auto:cdsdisk    -             ( datadg )     online udid_mismatch c1t5006048C536979A0d66s2 lun WD srdf-r2
emc1_0074     auto:cdsdisk    -             ( datadg )     online udid_mismatch c1t5006048C536979A0d67s2 lun WD srdf-r2

# ./vxudidlist.sh | egrep 'emc0_008d|emc0_008e‘
emc0_008d dgname:datadg EMC%5FSYMMETRIX%5F000290300822%5F220008D000 EMC%5FSYMMETRIX%5F000290300822%5F220008D000   match
emc0_008e dgname:datadg EMC%5FSYMMETRIX%5F000290300822%5F220008E000 EMC%5FSYMMETRIX%5F000290300822%5F220008E000   match

Secondary (target) server:

 
# vxdisk - eo alldgs list | grep srdf
emc1_0073     auto:cdsdisk    -             ( datadg )     online udid_mismatch c1t5006048C536979A0d66s2 lun WD srdf-r2
emc1_0074     auto:cdsdisk    -             ( datadg )     online udid_mismatch c1t5006048C536979A0d67s2 lun WD srdf-r2

# ./vxudidlist.sh | egrep 'emc1_0073|emc1_0074‘
emc1_0073 dgname:datadg online EMC%5FSYMMETRIX%5F000290301414%5F1400073000 EMC%5FSYMMETRIX%5F000290300822%5F220008D000   mismatch
emc1_0074 dgname:datadg online EMC%5FSYMMETRIX%5F000290301414%5F1400074000 EMC%5FSYMMETRIX%5F000290300822%5F220008E000   mismatch

The above two EMC devices are reporting a udid_mismatch, as the SRDF-R2 target luns have inherited the on-disk UDID value from the source SRDF-R1 luns.