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@hp.com
Hewlett-Packard Industry Standard Server Storage Advanced Technology


From: owner-t10@t10.org [mailto:owner-t10@t10.org] On Behalf Of Larry Chen
Sent: Wednesday, January 09, 2008 3:35 PM
To: Kevin D Butt
Cc: t10@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@us.ibm.com]
Sent: Wednesday, January 09, 2008 8:15 AM
To: Larry Chen
Cc: t10@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@us.ibm.com
http://www-03.ibm.com/servers/storage/

"Larry Chen" <Larry_Chen@pmc-sierra.com>
Sent by: owner-t10@t10.org

01/08/2008 03:00 PM

To

<t10@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).