SAS2 - OPEN TIMEOUT

Elliott, Robert (Server Storage) Elliott at hp.com
Wed Jan 9 17:18:10 PST 2008


Formatted message: <A HREF="r0801096_f.htm">HTML-formatted message</A>

1. The name in 4.5 is incorrect.  "open connection timeout occurs" should be
"Open Timeout timer expires (see 7.12.2)".  I'll mark that for sas2r14.
2. The rule in the port layer is only optional if there is no I_T Nexus Loss
timer.	If there is one, then Retry Open is processed as a Retry Open.	Mode
pages are optional in targets, so the target might not implement the timer. 
In initiators, there are no mode pages, so it's just a "should" that the
initiator implement an I_T Nexus Loss timer using the same value as the
target to which it is talking (see 8.2.2.3.1 and table 151 in 8.2.2.1).
--
Rob Elliott, elliott at hp.com
Hewlett-Packard Industry Standard Server Storage Advanced Technology
________________________________
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Sheffield,
Bob
Sent: Wednesday, January 09, 2008 5:35 PM
To: Larry Chen; Kevin D Butt
Cc: t10 at t10.org
Subject: RE: SAS2 - OPEN TIMEOUT
This discussion raises a more basic question for me: does the term, "open
connection timeout" mean the same thing as "Connection Timeout Timer
expires"? The term, "open connection timeout" occurs only once in the entire
standard (in subclause 4.5), whereas the term "Open Timeout Timer expires"
occurs 7 times in the text. The latter is what happens when the attached phy
doesn't send an ARB for 1ms. There is a corresponding confirmation from the
link layer to the port layer, "Open Timeout Occurred", which sounds a lot
like "open connection timeout", but is not explicitly equivalent.
Subclause 8.2.2.3.2 PL_OC2:Overall_Control state establishing connections
states:
If this state receives a Retry Open (No Destination) or a Retry Open (Open
Timeout Occurred) message and an I_T Nexus Loss timer has not been created
for
the destination SAS address (e.g., an SSP target port does not support the
I_T
NEXUS LOSS TIME field in the Protocol-Specific Port mode page or the field is
set to 0000h), then this state shall process the Retry Open message as either
a
Retry Open message or an Unable To Connect message. This selection is
vendor-specific.
Indicating it may be optional whether to retry or not. This behavior is at
the port level, so it applies not only to initiator ports, but also to target
ports and expander ports. I could see different port types needing to handle
this differently.
Incidently, a self-configuring expander has a way to report this condition to
a management application, "Connection request failed: Open Timeout timer
expired" (see table 235 in subclause 10.4.3.5.4 Self-configuration status
descriptor).
Bob Sheffield
LSI Corporation
________________________________
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Larry Chen
Sent: Wednesday, January 09, 2008 2:35 PM
To: Kevin D Butt
Cc: t10 at t10.org
Subject: RE: SAS2 - OPEN TIMEOUT
IMO, Timeouts are more serious than OPEN_REJECTs (and NAK, SCSI Busy and Full
Queue) Responses.
If Timeouts are _not_ reported to the host driver and/or the diagnostic
monitoring code then the problem can not
be detected and rectified Via a FRU swap.
________________________________
From: Kevin D Butt [mailto:kdbutt at us.ibm.com]
Sent: Wednesday, January 09, 2008 8:15 AM
To: Larry Chen
Cc: t10 at t10.org
Subject: Re: SAS2 - OPEN TIMEOUT
 I do not see a reason to distinguish an open timeout from the other errors. 
Unless there is a very good reason, I would prefer to leave the text as is. 
It seems to me that we should retry open timeouts, since it may work the next
time.  Also, the point of doing recovery operations is to mask errors (so
that the job can continue), so that does not seem like a good reason to stop
attempting the recovery.
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-2869 / 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at us.ibm.com
http://www-03.ibm.com/servers/storage/
"Larry Chen" <Larry_Chen at pmc-sierra.com>
Sent by: owner-t10 at t10.org
01/08/2008 03:00 PM
To
<t10 at t10.org>
cc
Subject
SAS2 - OPEN TIMEOUT
Is there any mechanism in place to _exclude_ OPEN TIMEOUT from being retried
(see
RED font below for details). I think there is a danger of masking out errors
if OPEN TIMEOUT
Is blindly retried.
---
4.5 I_T nexus loss
When a SAS port receives OPEN_REJECT (NO DESTINATION), OPEN_REJECT (PATHWAY
BLOCKED),
OPEN_REJECT (RESERVED INITIALIZE 0), OPEN_REJECT (RESERVED INITIALIZE 1),
OPEN_REJECT
(RESERVED STOP 0), OPEN_REJECT (RESERVED STOP 1), or an open connection
timeout occurs in
response to a connection request, it shall retry the connection request
until:
a) the connection is established;
b) for SSP target ports, the time indicated by the I_T NEXUS LOSS TIME field
in the Protocol-Specific Port
mode page (see 10.2.7.4) expires; or
c) the I_T nexus loss timer, if any, expires (see 4.7.1, 8.2.2.1, 10.2.7.4,
and 10.4.3.17).



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