SAS2 - OPEN TIMEOUT

Gerry.Houlder at seagate.com Gerry.Houlder at seagate.com
Wed Jan 9 15:08:32 PST 2008


* From the T10 Reflector (t10 at t10.org), posted by:
* Gerry.Houlder at seagate.com
*
SAS is set up so that repeated open timeouts will eventually result in I_T
nexus timeout, which will bring attention to the issue. The intent is that
a couple of open timeouts (which is only 1 Msec) might not be a serious
issue (e.g., device might be waking up from a low power mode and is still a
bit slow) but repeated timeouts are serious.
	     "Larry Chen"						   
	     <Larry_Chen at pmc-s						   
	     ierra.com> 						To 
	     Sent by:		       "Kevin D Butt" <kdbutt at us.ibm.com>  
	     owner-t10 at t10.org						cc 
	     No Phone Info	       <t10 at t10.org>			   
	     Available						   Subject 
				       RE: SAS2 - OPEN TIMEOUT		   
	     01/09/2008 03:35						   
	     PM 							   
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						   
									To 
 01/08/2008 03:00 PM					    <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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