Dynamic Multi-Pathing (DMP) works with the EMC Symmetrix disk array only if the disk array is configured in the Common Serial Number Mode [C-bit set]. Without this mode, DMP cannot provide multipathing functionality.

Until EMC Symmetrix started supporting devices above FFF, if digits 6 to 8 of the EMC Symmetrix disk serial number are zeroed out then the C-bit is set and the array is configured in the Common Serial Number Mode as required by DMP. But after EMC Symmetrix started supporting devices above FFF, they used the last bit to set it to 8 to represent a device above 0xFFF. This "8" is added with a logical "OR" operation so that you device would end with 378 (370 or 008) on port 7dA and 3A8 (3A0 or 008) on port 10dA.

With the "C" bit, the serial number must be identical (common) on all the ports. The "8" remains to represent a device above 0xFFF, the the rest is set to 0. 000 or 008 = 008.

The disk serial number can be obtained with various commands including the VERITAS vxdmpinq, vxdmpdebug command or the vxexplorer output.

/etc/vx/diag.d/vxdmpinq /dev/rdsk/c3t12d15s2
Vendor id :   EMC
Product id :  SYMMETRIX
Revision :     5266
Serial Number : 1004E000a

or

/etc/vx/diag.d/vxdmpinq /dev/rdsk/c3t5006048C52A820D6d766s2
Inquiry for /dev/rdsk/c3t5006048C52A820D6d766s2, evpd 0x0, page code 0x0
      Vendor id                        : EMC    
      Product id                        : SYMMETRIX      
      Revision                          : 5772
      Serial Number                  : 273E2008a

The serial number above shows that digits 6-8 are zeroed out. The array is setup in Common Serial Number Mode as required by DMP.

DMP needs to see identical device serial numbers from each path.
If the C-bit is not set then DMP sees multiple disks of the same device through different paths.
If the C-bit is set then DMP sees one unique disk device through multiple paths.

The layout for the EMC Symmetrix disk serial number is:

1004E000a (or)  273E2008a
SSVVVDDPx

SS = Last 2 digits of the Symmetrix serial number
VVV = Symmetrix volume number in hex. 000-FFF
DD = Director number [host adapter] 1-32
P = Port number on director card
x = lower case letter which does not belong to serial number according to EMC.

Note: If the C-bit is not set, data on an existing disk can easily be wiped out by disk operations to the other path which appears like a different disk all together. Setting the C-bit nulls out digits 6 through 8 of the serial number.

Consult the Storage Foundation Hardware Notes for a complete list of DMP pre-requisites regarding EMC Symmetrix arrays.