SCSI-3 FCP ACA/QErr abort process

Charles Monia Monia at mail.dec.com
Mon Aug 25 08:30:00 PDT 1997


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Charles Monia <Monia at mail.dec.com>
*
-----Original Message-----
From:	Bob Snively [SMTP:Bob.Snively at Eng.Sun.COM]
Sent:	Monday, August 25, 1997 12:19 AM
To:	jnemeth at concentric.net; t10 at Symbios.COM
Subject:	Re: SCSI-3 FCP ACA/QErr abort process
[CAM]  < stuff deleted>
B)	Overlapped commands
	If I remember correctly (and this should be clearly laid out in
	SCSI-2 and more obtusely laid out in SCSI-3), the occurrence of
	a command to the same ITLQ nexus (having the same initiator, target,
	LUN, and queue tag) is an overlapped command.  Since this is=20
	a software/firmware bug, the recovery is dramatic.  You terminate
	both commands asap,=20
[CAM] =20
[CAM]  That is correct, more specifically:
[CAM]  From SCSI-2 rev 10L, section 7.5.2, pp 80:=20
"A target that detects an incorrect initiator connection shall abort all =
I/O processes for the initiator on the logical unit or target routine =
and shall return CHECK CONDITION status. The sense key shall be set to =
ABORTED COMMAND
and the additional sense code shall be set to OVERLAPPED COMMANDS =
ATTEMPTED."=20
t
[CAM]  From "SAM" rev 18, pp 53:
"5.6.2 Overlapped Commands
An overlapped command occurs when an application client reuses a task =
address in a new command while a previous command to which that address =
was assigned is still pending as specified in 5.4. (The format of a task =
address is described in object definition 7.)
Each SCSI-3 protocol standard shall specify whether or not a logical =
unit is required to detect overlapped commands. A logical unit that =
detects an overlapped command shall abort all tasks for the initiator in =
the task set and shall return CHECK CONDITION status for that =
command...."
Both of these are identical in substance.  ie.  The occurance of an =
overlapped command is equivalent to an ABORT TASK SET (see SAM =
definition below)
>From SAM, section, 6, pp 58.
"ABORT TASK SET( Logical Unit Identifier || ) - Abort all tasks in the =
task set for the requesting initiator."
[CAM] =20
C)	QErr aborts
=20
       In parallel SCSI, they are silent.  In FCP, they are optionally
	silent, but 7.1.2.5 allows the recovery abort to be performed if
	there is any question about resources being partially cleared up.
[CAM]  The recovery abort is transport layer stuff. From the standpoint =
of the Class Driver (the generic O/S driver), that sort of cleanup at =
the transport layer is invisible.=20
Regards,
Charles
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