SAS: transport layer: ACK lost

Seto, Pak-lung pak-lung.seto at intel.com
Wed Jul 12 05:38:58 PDT 2006


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George,
It retry data needs to be re-written even if it has been ACKed, then the
SAS standard needs to clearly specify that because I don't see anywhere
in the standard said the retried data need to overwrite the old data - I
don't believe this is how some of the existing implementations are
implemented as you described, because it is very difficult to walk thru
the host buffer scatter gather list (usually this is how host buffers
are being implemented) at the retried data offset point when data frame
is retried by the target - it is not impossible, it is just added
complexity for no obvious reason.  Don't think this is a problem for the
target, I believe it is a problem for the initiator receives read data
(retried read data) from the target.
Pak
________________________________
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Mignon
Fernandez
Sent: Wednesday, July 12, 2006 2:16 AM
To: George Penokie
Cc: t10 at t10.org
Subject: RE: SAS: transport layer: ACK lost
Hello Mr. Penokie, 
Thank you for your response.  Yes, I was assuming frame level retries
are enabled and was referring to handling of retried data in general
(initiator's or target's point of view). 
Regards,
Mignon 
________________________________
From: George Penokie [mailto:gop at us.ibm.com] 
Sent: Thursday, July 06, 2006 2:35 PM
To: Mignon Fernandez
Cc: t10 at t10.org
Subject: Re: SAS: transport layer: ACK lost
Mignon, 
>From your question it is not clear if you are asking from a targets
point of view or an initiators point of view. It's also not clear if you
are asking about what happens if frame level retries are enabled or
disabled. 
So given that lack of knowledge the answer to you question is yes you
have to overwrite data that is retried even if it has been ACKed. 
Bye for now,
George Penokie
Dept 9A8 030-3 A410
E-Mail:    gop at us.ibm.com
Internal:  553-5208
External: 507-253-5208 
"Mignon Fernandez" <Mignon.M.Fernandez at bitmicro.com> 
Sent by: owner-t10 at t10.org 
06/21/2006 08:00 AM 
To
<t10 at t10.org> 
cc
Subject
SAS: transport layer: ACK lost
Hello, 
If retries are enabled, and an ACK gets lost, then the transmitter
retries, is it required for the receiver to overwrite the data that is
retried even if it has ACK-ed all data in the previous connection? 
Thanks in advance, 
Mignon Fernandez 



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