TAS bit or other mechanisms

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Wed Feb 6 08:43:01 PST 2008


* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
*
The traditional method for a SCSI device to report this is to wait for a
new command from an
initiator that had commands aborted and return CHECK CONDITION status and
sense bytes of
either RESET OCCURRED or COMMANDS CLEARED BY ANOTHER INITIATOR. This
requires an initiator to send another command (e.g., TEST UNIT READY) when
it thinks one
or more commands are overdue. The returned sense bytes should at least tell
you why the
commands won't complete and provide the clue that the commands must be
resent. Don't
blindly send another reset in this case, that just makes things worse.
The TAS bit was added to SCSI in response to request from folks that use a
bridge from some
interfaces (like 1394) where the loss of commands was troublesome and the
SCSI unit attention
for "commands cleared by another initiator" wasn't good enough
notification.
	     "Alan Gess"						   
	     <agess at istor.com>						   
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								   Subject 
				       TAS bit or other mechanisms	   
	     02/05/2008 04:49						   
	     PM 							   
* From the T10 Reflector (t10 at t10.org), posted by:
* "Alan Gess" <agess at istor.com>
*
Hello,
One issue that I have come across over the years with SCSI is the "ping
pong" of hard resets with a device that has multiple initiators issuing
tasks to it. This occurs when one initiator reset the devices while
another initiator has tasks outstanding to the same device. I am sure
you all know about this issue.
I see a TAS (Task Abort Status) bit was added to help resolve this issue
but after testing four different manufactures of drives, only one
supports it.
My question: Is there another mechanism in place to prevent this or does
anyone have any ideas on how to overcome this issue?
Thanks,
Alan Gess
iStor Networks, Inc.
agess at istor.com
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