SAS2 - OPEN TIMEOUT

Elliott, Robert (Server Storage) Elliott at hp.com
Wed Jan 9 14:58:47 PST 2008


Formatted message: <A HREF="r0801093_f.htm">HTML-formatted message</A>

The OPEN is not blindly retried - it's retried only until the I_T Nexus Loss
Time timer expires (normally 2 seconds).
The most likely reason for Open Timeout timer expiration is that the OPEN
address frame suffered a single-bit error.  Since there is no ACK/NAK for
address frames, the only indication of a problem is the lack of an AIP,
OPEN_ACCEPT, or OPEN_REJECT.  The originator times out after 1 ms and retries
(so a single-bit error doesn't cause a major error).
If the bit error keeps occuring, though, the I_T Nexus Loss Time will kick in
and a major error will be reported (the destination is unreachable).
--
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 Larry Chen
Sent: Wednesday, January 09, 2008 3:35 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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