Transport layer retries

Sheffield, Robert L robert.l.sheffield at intel.com
Tue Aug 9 09:43:21 PDT 2005


* From the T10 Reflector (t10 at t10.org), posted by:
* "Sheffield, Robert L" <robert.l.sheffield at intel.com>
*
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Now that I think about it - it might not be a bad idea to define an
"INITIATOR SUPPORTS TLR" bit in the SAS command frame. A value of zero
wouldn't require that the target NOT attempt retries, but it would be a
pretty good hint that it's not such a good idea.=20
=20
Does this sound like a reasonable approach?
=20
Bob

  _____ =20

From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Day,
Brian
Sent: Tuesday, August 09, 2005 8:13 AM
To: 'Bill Martin'; t10 at t10.org
Subject: RE: Transport layer retries


Bill...
=20
If you follow the tables listed in the state machines (particularly
tables 130, 133, and 134) in section 9.2.6, I believe you will see that
an initiator that doesn't support retries will turn the target's =
attempt
of the retry into a Command Complete Received confirmation to the app
layer, with the appropriate delivery result error argument.
This would then cause the application layer (section 10.2.2) to send
down an ABORT TASK.
=20
However, an initiator should not be NAKing frames just because it does
not support transport retries... it should only for link errors. =20
=20
Hope this helps...
=20
Brian Day
LSI Logic

  _____ =20

From: Bill Martin [mailto:bill_martin at sierralogic.com]=20
Sent: Tuesday, August 09, 2005 8:19 AM
To: t10 at t10.org
Subject: Transport layer retries



SAS 1.1 allows for discovery of whether a target supports transport
layer retries, but in the spirit of SCSI, the standard does not require
that the mode page bit be changeable.  In the event that the mode page
bit is not changeable, and the initiator does not support transport
layer retries, what is the mechanism for stopping continuous retries by
the target until a timeout occurs?  The definition of the retry
mechanism in 9.2.4.4.2 and 9.2.4.5.2 require that if retransmitted =
frame
is received the initiator shall operate on it properly.  Finally, the
number of times that a frame will be retransmitted is vendor specific,
so if the initiator sends NAK, it may be retried over and over.

=20

Thanks for any insight.

=20

Bill Martin
Sr. Principal Engineer
Standards and Interoperability
Sierra Logic, Inc.
916 772-3658

916 765-6875 (Cell)
bill_martin at sierralogic.com

=20


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<DIV dir=3Dltr align=3Dleft><SPAN class=3D094372816-09082005><FONT =
face=3DArial=20
color=3D#0000ff size=3D2>Now that I think about it - it might not be a =
bad idea to=20
define an "INITIATOR SUPPORTS TLR" bit in the SAS command frame. A =
value of zero=20
wouldn't require that the target NOT attempt retries, but it would be a =
pretty=20
good hint that it's not such a good idea. </FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D094372816-09082005><FONT =
face=3DArial=20
color=3D#0000ff size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D094372816-09082005><FONT =
face=3DArial=20
color=3D#0000ff size=3D2>Does this sound like a reasonable=20
approach?</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D094372816-09082005><FONT =
face=3DArial=20
color=3D#0000ff size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D094372816-09082005><FONT =
face=3DArial=20
color=3D#0000ff size=3D2>Bob</FONT></SPAN></DIV><BR>
<DIV class=3DOutlookMessageHeader lang=3Den-us dir=3Dltr align=3Dleft>
<HR tabIndex=3D-1>
<FONT face=3DTahoma size=3D2><B>From:</B> owner-t10 at t10.org=20
[mailto:owner-t10 at t10.org] <B>On Behalf Of </B>Day, =
Brian<BR><B>Sent:</B>=20
Tuesday, August 09, 2005 8:13 AM<BR><B>To:</B> 'Bill Martin';=20
t10 at t10.org<BR><B>Subject:</B> RE: Transport layer =
retries<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D301530415-09082005><FONT =
face=3DArial=20
color=3D#800000 size=3D2>Bill...</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D301530415-09082005><FONT =
face=3DArial=20
color=3D#800000 size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D301530415-09082005><FONT =
face=3DArial=20
color=3D#800000 size=3D2>If you follow the tables listed in the state =
machines=20
(particularly tables 130, 133, and 134) in section 9.2.6, I believe you =
will see=20
that an initiator that doesn't support retries will turn&nbsp;the =
target's=20
attempt of the retry into a Command Complete Received confirmation to =
the app=20
layer, with the appropriate delivery result=20
error&nbsp;argument.</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D301530415-09082005><FONT =
face=3DArial=20
color=3D#800000 size=3D2>This would then cause the application layer =
(section=20
10.2.2) to&nbsp;send&nbsp;down an&nbsp;ABORT TASK.</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN =
class=3D301530415-09082005></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D301530415-09082005><FONT =
face=3DArial=20
color=3D#800000 size=3D2>However, an initiator should not =
be&nbsp;NAKing=20
frames&nbsp;just because it does not support transport retries... it =
should only=20
for link&nbsp;errors.&nbsp;&nbsp;</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D301530415-09082005><FONT =
face=3DArial=20
color=3D#800000 size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D301530415-09082005><FONT =
face=3DArial=20
color=3D#800000 size=3D2>Hope this helps...</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D301530415-09082005><FONT =
face=3DArial=20
color=3D#800000 size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D301530415-09082005><FONT =
face=3DArial=20
color=3D#800000 size=3D2>Brian Day</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D301530415-09082005><FONT =
face=3DArial=20
color=3D#800000 size=3D2>LSI Logic</FONT></SPAN></DIV><BR>
<DIV class=3DOutlookMessageHeader lang=3Den-us dir=3Dltr align=3Dleft>
<HR tabIndex=3D-1>
<FONT face=3DTahoma size=3D2><B>From:</B> Bill Martin=20
[mailto:bill_martin at sierralogic.com] <BR><B>Sent:</B> Tuesday, August =
09, 2005=20
8:19 AM<BR><B>To:</B> t10 at t10.org<BR><B>Subject:</B> Transport layer=20
retries<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=3DSection1>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">SAS 1.1 allows for =
discovery of=20
whether a target supports transport layer retries, but in the spirit of =
SCSI,=20
the standard does not require that the mode page bit be =
changeable.&nbsp; In the=20
event that the mode page bit is not changeable, and the initiator does =
not=20
support transport layer retries, what is the mechanism for stopping =
continuous=20
retries by the target until a timeout occurs?&nbsp; The definition of =
the retry=20
mechanism in 9.2.4.4.2 and 9.2.4.5.2 require that if retransmitted =
frame is=20
received the initiator shall operate on it properly.&nbsp; Finally, the =
number=20
of times that a frame will be retransmitted is vendor specific, so if =
the=20
initiator sends NAK, it may be retried over and=20
over.<o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Thanks for any=20
insight.<o:p></o:p></SPAN></FONT></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial"><o:p>&nbsp;</o:p></SPAN></FONT></P>
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tabIndex=3D0 w:st=3D"on"><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Bill=20
Martin</SPAN></FONT></st1:PersonName><BR><FONT face=3DArial =
size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">Sr. Principal =
Engineer<BR>Standards=20
and Interoperability<BR>Sierra Logic, Inc.<BR>916=20
772-3658</SPAN></FONT><o:p></o:p></P>
<P class=3DMsoNormal><FONT face=3DArial size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: Arial">916 765-6875=20
(Cell)<BR>bill_martin at sierralogic.com</SPAN></FONT><FONT face=3DArial =
size=3D2><SPAN=20
style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial"><o:p></o:p></SPAN></FONT></P>
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