DPO bit in sample CDB

Kevin D Butt kdbutt at us.ibm.com
Wed Aug 24 10:39:34 PDT 2011

Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1108240_f.htm">HTML-formatted message</a>

I stumbled onto bits in the type variable length CDB for long LBA 32-byte 
commands that are not defined.
I sent the following note to Ralph:
In SPC-4r31, Table 17 -Typical variable length CDB for long LBA 32-byte 
commands in byte 10 bit 4 there is a DPO field and in bit 3 there is a FUA 
field.	There is no description for what these fields mean.  I can search 
for FUA and find it being used in multiple places. 
When I search for DPO I cannot find a single instance.
His response was that he suspects they are from SBC-3.
Indeed, I can find them defined in SBC-3.
The problem I still have, however, is that they are shown in Table 17 - 
Typical variable length CDB for long LBA 32-byte commands but there is not 
definition of what the bits mean.  While I don't like that the bits aren't 
described for the table, the FUA didn't bother me too much, because I 
could find it in a search of SPC-4.  However, not being able to find the 
DPO bit in SPC-4 left me lost and confused.  What should be done to remove 
that confusion?  Should there be a reference to the bits and where they 
can be found or should the offending bits be replaced with "device type 
specific info"?
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
Data Protection & Retention
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com

More information about the T10 mailing list