Elliott, Robert (Server Storage) Elliott at
Wed Jun 3 09:46:07 PDT 2009

* From the T10 Reflector (t10 at, posted by:
* "Elliott, Robert (Server Storage)" <Elliott at>
During discussion of Mark Evans' proposal 09-087r2 at the last CAP WG meeting
to improve the standardese wording for the SPC-4 SEND DIAGNOSTIC command's
DEVOFFL and UNITOFFL bits, I did a web search to see how implementations have
actually been interpreting them.  It appears that few are using these bits as
Their original definition was: 
- DEVOFFL means the test is allowed to take the entire SCSI target device
- UNITOFFL means the test is allowed to take the logical unit offline (but
not affect other logical units in the SCSI target device)
I think it might be best to redefine these bits as "vendor-specific" to
reflect their real usage. 
Some example real usages:
1. IBM TotalStorage LTI Ultrium Tape Drive SCSI Reference at  Page 107 says DevOfl and
UnitOfl (sic) are "any value allowed and ignored" 
2. Exabyte Mammoth-2 tape drive SCSI reference at
2719195.  Page 201 shows these combinations: 
DevOffL UnitOffL 
0	0	  Code check 
0	1	  Code check 
1	0	  Buffer check 
1	1	  Tape operation check 
3. STEC ZeusIOPS FC SSD Product Manual at
_Product_Manual.pdf. Page 63 shows these combinations: 
DevOffL  UnitOffL 
0	 1	   do long self test (< 90 sec) 
1	 0	   do short self test (< 2 sec) 
4. Quantum DLT 7000 Tape Drive Product Manual at	Page 206 has
a table: 
DevOfL	UnitOfL 
0	0	Self-test 1 
0	1	Self-test 2 
1	0	Self-test 1 
1	1	Self-test 2 
5. has the DevOfL
and UnitOfL descriptions backwards.
Rob Elliott, HP Industry Standard Server Storage
* For T10 Reflector information, send a message with
* 'info t10' (no quotes) in the message body to majordomo at

More information about the T10 mailing list