314 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
7.8.23  Tracing a volume from a host back to its physical disks
In some cases, you might need to verify exactly which physical disks are used to store data of 
a volume. This information is not directly available to the host; however, it might be obtained 
by using a sequence of queries. 
The first step is to unequivocally map a logical device seen by the host to a volume that is 
presented by the storage system. The best volume characteristics for this purpose is the 
volume ID. This ID is available to the operating system in the Vendor Specified Identifier field 
of page 0x80 or 0x83 (vital product data, VPD), which the storage device sends in response 
to SCSI INQUIRY command from the host. 
In practice, the ID can be obtained from the multipath driver in the operating system. After the 
volume ID is known, it can be used to identify physical location of data. 
On hosts that are running IBM System Storage Multipath Subsystem Device Driver, you can 
obtain the volume ID from the output of the datapath query device command. You see a long 
disk serial number for each vpath device, as shown in Example 7-37.
Example 7-37   The datapath query device command
DEV#:   0  DEVICE NAME: Disk1 Part0  TYPE: 2145       POLICY: OPTIMIZED
SERIAL: 60050768018301BF2800000000000005
============================================================================
Path#            Adapter/Hard Disk        State  Mode       Select     Errors
    0     Scsi Port2 Bus0/Disk1 Part0     OPEN   NORMAL         20          0
    1     Scsi Port3 Bus0/Disk1 Part0     OPEN   NORMAL       2343          0
DEV#:   1  DEVICE NAME: Disk2 Part0  TYPE: 2145       POLICY: OPTIMIZED
SERIAL: 60050768018301BF2800000000000004
============================================================================
Path#            Adapter/Hard Disk        State  Mode       Select     Errors
    0     Scsi Port2 Bus0/Disk2 Part0     OPEN   NORMAL       2335          0
    1     Scsi Port3 Bus0/Disk2 Part0     OPEN   NORMAL          0          0
DEV#:   2  DEVICE NAME: Disk3 Part0  TYPE: 2145       POLICY: OPTIMIZED
SERIAL: 60050768018301BF2800000000000006
============================================================================
Path#            Adapter/Hard Disk        State  Mode       Select     Errors
    0     Scsi Port2 Bus0/Disk3 Part0     OPEN   NORMAL       2331          0
    1     Scsi Port3 Bus0/Disk3 Part0     OPEN   NORMAL          0          0
Note: For sequential and image mode volumes, a volume copy is mapped to exactly one 
MDisk. This configuration often is not the case for stripped volumes, unless volume size is 
not greater than an extent size. Therefore, a single stripped volume uses multiple mDisks 
in a typical case.
State: In Example 7-38, the state of each path is OPEN. Sometimes, the state is CLOSED. 
This state does not necessarily indicate a problem because it might be a result of the 
path’s processing stage.