Interaction between untagged task and simple task?

Ralph Weber ralphoweber at
Fri Jul 25 17:00:41 PDT 2003

* From the T10 Reflector (t10 at, posted by:
* Ralph Weber <ralphoweber at>

The following two cases are identical:

write   (untagged)          write   (simple)
inquiry (simple)            inquiry (simple)
write   (untagged)          write   (simple)

The only difference between the two cases is that
the case on the left cannot have both write commands
in the task set at the same time, whereas the case
on the right might describe the total contents of
a task set.

You have, in fact, found the SAM-3 statement that defines
the behavior:

    "... and implicitly a SIMPLE task attribute ..."

While I am not advocating any specific implementations,
a legitimate implementation for untagged tasks is to
assign them the SIMPLE task attribute and an impossibly
large tag value (e.g., 0xFFFFFFFFFFFFFFFFFFFF).

Hope this helps,


Kevin D Butt wrote:

 > What is the interaction between untagged and simple tasks from the
 > same initiator supposed to be?
 > As an example:
 > write (untagged)
 > inq (simple)
 > write (untagged)
 > I have searched the standards (SAM-2) and did not find any reference
 > to the interaction between an untagged task and a simple tagged task.
 > In describing an untagged task clause 4.9.1 states:
 > An untagged task is represented by an I_T_L nexus (see 4.10) and is
 > composed of a definition of the work to be performed by the logical
 > unit, and implicitly a SIMPLE task attribute (see 7.5).
 >  and
 > An untagged task does not include a tag in its I_T_L nexus, thus
 > restricting the number of concurrent untagged tasks in a single task
 > set to one per initiator. Also, an untagged task is assumed to have a
 > SIMPLE task attribute, leaving the initiator no control over its
 > relationship to other tasks in the task set.
 > I can guess that a simple tagged task can be processed after an
 > untagged task begins but that an untagged task received after a simple
 > tagged task begins and before it completes must get an overlapped
 > command check condition.  However, I am just guessing that this is wha
 > the behavior should be.
 > Can anybody enlighten me?
 > Thanks,
 > Kevin D. Butt
 > Fibre Channel & SCSI Architect, IBM Tape Microcode,
 > 6TYA, 9000 S. Rita Rd., Tucson, AZ  85744
 > Tie-line 321; Office: 520-799-5280, Lab: 799-5751, Fax: 799-4138,
 > Email: kdbutt at

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