Interpretation of Logical unit Reset behavior

Bill Galloway BillG at breatech.com
Fri Oct 18 15:43:07 PDT 2002


* From the T10 Reflector (t10 at t10.org), posted by:
* "Bill Galloway" <BillG at breatech.com>
*
Gerry,

I believe both are correct.  The transfer agreement is with the target
not the lun.  You can do a full power-on reset of the lun if you want to
but that does not reset the target.  Disk drives are a special case
because they have only one lun and it is easy to confuse a target and
lun.  The logical unit reset does not effect the transfer agreement
between the target and initiator. The use of the words "device power-on"
in sam is unfortunate but not incorrect.  There are targets that map
totally separate devices behind luns.  In this case you are resetting
the "device".

Bill Galloway
BREA Technologies, Inc.
P: (281) 530-3063
F: (281) 988-0358
BillG at breatech.com 

-----Original Message-----
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of
gerry.houlder at seagate.com
Sent: Friday, October 18, 2002 4:26 PM
To: t10 at t10.org
Subject: Interpretation of Logical unit Reset behavior


* From the T10 Reflector (t10 at t10.org), posted by:
* gerry.houlder at seagate.com
*
A contradiction has been pointed out for the description of the Logical
Unit Reset behavior. In particular, note the requirements I have marked
with double brackets << >>.

>From SPI - 4 or 5:

   16.5.6 LOGICAL UNIT RESET
   The LOGICAL UNIT RESET message is defined in the SCSI Architecture
   Model-2 standard.
   Receipt of the LOGICAL UNIT RESET message after an I_T_L nexus has
been
   established is a logical
   unit reset event as defined in the SCSI Architecture Model-2
standard.
   In addition to the requirements in the SCSI Architecture Model-2
   standard the SCSI target port shall go to
   the BUS FREE phase following the successful receipt of the LOGICAL
UNIT
   RESET message.

   <<A logical unit reset has no effect on the transfer agreement.>>

>From SCSI Architecture Model-2 standard

   5.9.7 Logical unit reset
   A logical unit reset is:
   a) The action in response to a LOGICAL UNIT RESET task management
   request (see 6.6) or some other
   logical unit reset event; or
   b) One of the actions in response to a TARGET RESET task management
   function (see 6.7) or a hard reset
   (see 5.9.6).
   The definition of logical unit reset events is dependent on the SCSI
   transport protocol.
   To process a logical unit reset the logical unit shall:
   a) Abort all tasks as described in 5.7;
   b) Clear a CA (see 5.9.1.6) or ACA (see 5.9.1.7) condition, if one is
   present;
   c) Release all reservations established using the reserve/release
   management method (persistent reserva-tions
   shall not be affected);
   <<d) Return the logical unit's operating mode to the appropriate
initial
   conditions, similar to those conditions that
   would be found following device power-on.>> The MODE SELECT
parameters
   (see SPC-2) shall be restored
   to their last saved values if saved values have been established.
MODE
   SELECT parameters for which no
   saved values have been established shall be returned to their default
   values;
   e) Set an unit attention condition (see 5.9.5); and
   f) Initiate a logical unit reset for all dependent logical units (see
   4.13).
   In addition to the above, the logical unit shall perform any
additional
   functions required by the applicable standards.

The wording from SPI says "no effect on transfer agreement", meaning the
target has to remember the transfer agreement even though everything
else is being reset. The SAM wording says "similar to power on", which
certainly includes resetting the transfer agreement. These conditions
certainly conflict with each other. How do we resolve the conflicting
wording?

The single LUN targets I am familiar with reset all the same things
(including the transfer agreement) for both of these functions. Are
these devices in violation of the standard?

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