Subject: StatSN and overlapped commands
Message-ID: <OF7727DEFB.1114C870-ON85256D79.004A2144@attotech.com>
Date: Tue, 5 Aug 2003 09:45:43 -0400
MIME-Version: 1.0
Content-type: text/plain; charset=us-ascii
To: ips@ece.cmu.edu
From: dcuddihy@attotech.com
Sender: owner-ips@ece.cmu.edu
Precedence: bulk

I have a question about the lifespan of SCSI tasks on ISCSI.  My apologies
if it's been addressed on the reflector previously.

Put simply, is a SCSI task considered completed when status is returned to
the initiator, or when status is acknowledged via ExpStatSN?

This causes a difference in behavior for untagged SCSI commands.  Consider:

Initiator: SCSI Command = Write: Attr = Untagged (0) : InitiatorTaskTag=5:
CmdSN=4: ExpStatSn = 3
Target:  R2T: InitiatorTaskTag = 5
Initiator: SCSI Data: Initiator Task Tag = 5
Target: SCSI Status = Good:  Initiator Task Tag = 5: StatSn = 3
Initiator: Scsi Command = Write: Attr = Untagged (0) : Initiator Task Tag
= 6: CmdSN=5: ExpStatSn = 3
.
.
(Somewhere down the line a scsi command with ExpStatSN of 4 is sent, ACKing
the Status to ITT #5)
.
.

Is this an overlapped command error, since the SCSI task is still
oustanding until the status is acknowledge?
Or -- is the SCSI command considered completed as soon as status is
attempted (much like the clearing of a Congingent Allegiance as soon as
status is started to the host)?  That would mean that this is a legal
exchange.  If so, does this cause problems with command recovery as
described in section 3.2.2.2 ?

Thanks!

david



David J Cuddihy
Principal Engineer
ATTO Technology, Inc.
http://www.attotech.com/fcbridge.html
dcuddihy@attotech.com