A SAS Outstanding Xfer_RDY Question.

Evans, Mark Mark_Evans at maxtor.com
Tue Jul 1 10:35:56 PDT 2003


* From the T10 Reflector (t10 at t10.org), posted by:
* "Evans, Mark" <Mark_Evans at maxtor.com>
*
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Hi Bob,
 
Though in principle I agree with George that there is no need for any
other mechanism, I'd be happy to support your solutions 1 (obsolete the
field), 3 (make it a fixed value) so long as the fixed value is 0000h,
or 4 (the value of first burst shall not be settable by MODE SELECT).
I'm sure we can resolve this at the SAS protocol working group meeting
next week.
 
Regards,
 
Mark Evans
Maxtor Corporation
408-894-5310
 
-----Original Message-----
From: Nixon, Bob [mailto:Bob.Nixon at emulex.com]
Sent: Tuesday, July 01, 2003 9:14 AM
To: 'George Penokie'
Cc: t10 at t10.org
Subject: RE: A SAS Outstanding Xfer_RDY Question.
 
"...things will get ugly real quick but so be it..."
 
George, this is not an acceptable answer for a commercial product.
Given the current SAS standard:
 
1)  There is no reason to expect various initiators to coordinate
setting of first burst.
 
2)  In fact, this very issue will lead them NOT to...each initiator may
see some advantage (a hair better performance, an increase in stability)
to choosing their own value (or zero) for first burst.
 
3 The result of my not designing for noncoordinated settings is that MY
initiator will hang.  Doesn't matter whose fault it is, in the eyes of
the customer.  In fact, if I don't design for the worst case, it IS my
fault.
 
4) Designing for the worst case as pointed out earlier in this thread
requires active assurance that the setting of first burst is at least
known before every comand is sent.  Since this involves awareness of
unit attentions and sending of MODE SENSE/SELECT commands, the transport
layer becomes highly tangled with the application.  This was exactly
what 02-403 was intended to untangle, but I believe it didn't go far
enough.
 
5)  As Rob pointed out, I can't simplify by forcing my own preferred
value:  I have to be able to detect and support first burst of whatever
current size in order to change first burst to my preferred size.
 
6)  SPC-3 hints that using first burst of zero to disable first burst is
an unacceptable solution...in the specification of the first burst field
it says "SCSI transport protocols supporting this field shall provide an
additional mechanism to enable and disable the first burst function."
Additional to what?  The only reasonable interpretation of the adjective
"additional" in this context is "other than the mode page setting".  SAS
does not provide such an additional mechanism, so I would claim it is
out of compliance with SPC-3.
 
7)  FCP-2 provides an "additional mechanism" as a flag during login.
Then the PLDA interoperability profile requires that flag to be set so
as to prohibit using first burst at all.  Given the above, this is no
surprise, and the precedent should be considered carefully by SAS.  The
major vendors of FCP equipment still are able to demonstrate 99%+ of
theoretical performance, so the value-add of the first burst feature is
highly suspect.
 
Taking all that into consideration, my company and I would strongly
recommend that one of the following resolutions be incorporated in SAS
1.1 (in our preference order):
 
1)  Obsolete first burst.
 
2)  Provide a true "additional mechanism" to disable it on a per
initiator basis.  Our proposal to do it with a flag in the COMMAND IU is
one such mechanism.
 
3)  Make first burst a fixed value by standard (e.g., "the value of
first burst shall be 10000h").
 
4)  As a marginally acceptable resolution, make first burst a fixed
property of the target (i.e., "the value of first burst shall not be
settable by MODE SELECT).
 
   - Bob
 
 
-----Original Message-----
From: George Penokie [mailto:gop at us.ibm.com]
Sent: Tuesday, July 01, 2003 6:24 AM
To: Nixon, Bob
Cc: t10 at t10.org
Subject: RE: A SAS Outstanding Xfer_RDY Question.

Bob, 

A value of zero in the first burst size field in the
disconnect/reconnected mode page turns off first burst. There is no need
for any other mechanism. If initiators start making changes to mode
pages without cooperation from other initiators things will get ugly
real quick but so be it, that's the way mode pages work and have always
worked. There are many examples of this with first burst only being one.
I believe the way it is defined is just fine and that adding anything to
the command to turn it on/off would only add complexity with no added
practical value.

Bye for now,
George Penokie

Dept 2C6  114-2 N212
E-Mail:    gop at us.ibm.com
Internal:  553-5208
External: 507-253-5208   FAX: 507-253-2880





 
"Nixon, Bob" <Bob.Nixon at emulex.com> 
Sent by: owner-t10 at t10.org 
06/30/2003 03:51 PM 
        
        To:        t10 at t10.org 
        cc:         
        Subject:        RE: A SAS Outstanding Xfer_RDY Question. 



* From the T10 Reflector (t10 at t10.org), posted by:
* "Nixon, Bob" <Bob.Nixon at Emulex.Com>
*
How does an initiator indicate to a target whether to use first burst or
not?  

Both SAM-3 and SAS specify that the Send SCSI Command and SCSI Command
Received transport services include a parameter indicating whether first
burst is enabled or not.  The prior discussion in this thread makes it
obvious the choice of the initiator has to be communicated to the target
in
order that XFER_RDY can be sent when needed.

We could claim setting the first burst size to zero in the
disconnect-reconnect mode page accomplishes the necessary communication.
But this would lead to possibly disastrous inefficiency...the first
burst
size setting affects all initiators for a port and can be changed by any
of
them at any time.  Every initiator would have to assure the correct mode
page setting before every command.  The means of doing this are messy at
best.

FCP-2 is the only other protocol that I could find that supports first
burst.  It implements the required means to disable first burst by a
per-initiator login flag (though this falls a little short of the
per-command implication of the transport service specification in
SAM-3).  I
would recommend SAS 1.1 meet the requirement by adding a bit to the SSP
COMMAND IU indicating whether the target is to honor (bit=0) or ignore
(bit=1) first burst size for the command.

I'll write this up for next week unless one of you educates me before
then.


  - Bob

-----Original Message-----
From: Evans, Mark [mailto:Mark_Evans at maxtor.com]
Sent: Friday, June 27, 2003 2:29 PM
To: 'Sheffield, Robert L'; t10 at t10.org
Subject: RE: A SAS Outstanding Xfer_RDY Question.


* From the T10 Reflector (t10 at t10.org), posted by:
* "Evans, Mark" <Mark_Evans at maxtor.com>
*
Hi Bob,

If the value in the FIRST BURST SIZE field is not zero, all of the rules
for
first burst are the same as for an XFER_RDY, that is, a SAS target port
shall not send an XFER_RDY until all of the data for the first burst has
been sent.  This is explicit in the standard in 10.2.6.1.5 FIRST BURST
SIZE
field.  The following is the fourth paragraph in that clause:

"If the amount of data to be transferred for the command is less than
the
amount of data specified by the FIRST BURST SIZE field, the SSP target
port
shall not transmit an XFER_RDY frame for the command.  If the amount of
data
to be transferred for the command is greater than the amount of data
specified by the FIRST BURST SIZE field, the SSP target port shall
transmit
an XFER_RDY frame after it has received all of the data specified by the
FIRST BURST SIZE field from the initiator.  All data for the command is
not
required to be transferred during the same connection in which the
command
is transferred."

I guess we could make this stronger by changing, "...the SSP target port
shall transmit an XFER_RDY frame after it has received all of the data
specified by the FIRST BURST SIZE field..." to "...the SSP target port
shall
not transmit an XFER_RDY frame until it has received all of the data
specified by the FIRST BURST SIZE field...", but the first was intended
to
mean the second.

Regards,

Mark Evans
Maxtor Corporation

-----Original Message-----
From:                  Sheffield, Robert L
[mailto:robert.l.sheffield at intel.com] 
Sent:                 Friday, June 27, 2003 12:44 PM
To:                 t10 at t10.org
Subject:                 RE: A SAS Outstanding Xfer_RDY Question.

* From the T10 Reflector (t10 at t10.org), posted by:
* "Sheffield, Robert L" <robert.l.sheffield at intel.com>
*
I didn't see this the last time I looked into the question, but it does
look
like only one XFER_RDY can be outstanding at a time. I looked into it
before
because of a question about the first burst transfer, and what sort of
timeout might occur in case the first burst never completes. I assumed
that
since the first burst is an implicit XFER_RDY, that the timeout would be
the
same whether it's the first burst or a transfer associated with an
explicit
XFER_RDY (the Initiator Response Timeout timer). What I'm left wondering
now
is if the target must wait for the first burst transfer to complete
before
sending the first XFER_RDY? Is that the intent, and is is stated
anywhere?

Bob Sheffield

-----Original Message-----
From: Sriram Srinivasan [mailto:srirams at lsil.com]
Sent: Friday, June 27, 2003 11:31 AM
To: t10 at t10.org 
Subject: RE: A SAS Outstanding Xfer_RDY Question.


* From the T10 Reflector (t10 at t10.org), posted by:
* Sriram Srinivasan <srirams at lsil.com>
*

 If sas-r04a.pdf is the current SAS spec, I see that in "10.2.1.8
Receive 
Data-Out transport protocol service" it talks about limiting number of 
outstanding XFER_RDY frames per command to 1.  I don't see where it
allows 
more than 1 outstanding XFER_RDY frame per command.
 
 
 \Sriram\
 
" 
" * From the T10 Reflector (t10 at t10.org), posted by:
" * "Bill Galloway" <BillG at breatech.com>
" *
" I believe the current SAS spec allows more than one outstanding
XFER_RDY 
per
" command.  There was some talk of limiting this but it never went
anywhere.
" 
" Bill Galloway
" Pivot3, Inc.
" BillG at pivot3.com
" P: (281) 530-3063
" F: (281) 988-0398 
" 
" -----Original Message-----
" From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of
Whitehill,
" Cliff
" Sent: Friday, June 27, 2003 11:03 AM
" To: t10 at t10.org
" Subject: A SAS Outstanding Xfer_RDY Question.
" 
" 
" * From the T10 Reflector (t10 at t10.org), posted by:
" * "Whitehill, Cliff" <cwhitehi at lsil.com>
" *
" All,
" 
" My current understanding is that for SAS you can have only one
outstanding
" Xfer_RDY per command.  Is this true? If so, where does it say this in
the
" SAS specification?
" 
" Regards,
" 
" --------------------------------------------
" Clifford A. Whitehill
" Staff Systems Engineer
" LSI Logic Corp.
" 2001 Danfield Ct.
" Fort Collins, CO. 80525
" Tel: 970-206-5024
" Fax: 970-206-5244
" email: cliff.whitehill at lsil.com
" 
" *
" * For T10 Reflector information, send a message with
" * 'info t10' (no quotes) in the message body to majordomo at t10.org
" 
" *
" * For T10 Reflector information, send a message with
" * 'info t10' (no quotes) in the message body to majordomo at t10.org



----------------------------------------------------------------------
                "FORGET NOT THAT THE EARTH DELIGHTS TO FEEL YOUR BARE
FEET,
              AND THE WINDS LONG TO PLAY WITH YOUR HAIR"
                                         -Khalil Gibran

Sriram Srinivasan                       Sriram.Srinivasan at lsil.com
ASIC Design Engineer, LSI Logic,
2001 Danfield Ct.,
Phone: 970-206-5847
Fort Collins, CO 80525
FAX  : 970-206-5244
----------------------------------------------------------------------

*
* For T10 Reflector information, send a message with
* 'info t10' (no quotes) in the message body to majordomo at t10.org
*
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<p class=3DMsoNormal><span class=3DEmailStyle16><font size=3D2 =
color=3Dblack
face=3DHelvetica><span style=3D'font-size:10.0pt;mso-bidi-font-size:12.0=
pt;
font-family:Helvetica'>Hi Bob,<o:p></o:p></span></font></span></p>

<p class=3DMsoNormal><span class=3DEmailStyle16><font size=3D2 =
color=3Dblack
face=3DHelvetica><span =
style=3D'font-size:10.0pt;mso-bidi-font-size:12.0pt;
font-family:Helvetica'><![if =
!supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></span></font></span></p>=


<p class=3DMsoNormal><span class=3DEmailStyle16><font size=3D2 =
color=3Dblack
face=3DHelvetica><span =
style=3D'font-size:10.0pt;mso-bidi-font-size:12.0pt;
font-family:Helvetica'>Though in principle I agree with =
George</span></font></span><span
class=3DEmailStyle16><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;mso-bidi-font-size:12.0pt;font-family:Arial'> =
</span></font></span><font
size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial;
color:black'>that there is no need for any other =
mechanism,</span></font><span
class=3DEmailStyle16><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;mso-bidi-font-size:12.0pt;font-family:Arial'> =
</span></font></span><span
class=3DEmailStyle16><font size=3D2 color=3Dblack =
face=3DHelvetica><span
style=3D'font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family:Helvetic=
a'>I&#8217;d be
happy to support your solutions 1 (obsolete the field), 3 (make it a =
fixed
value) so long as the fixed value is 0000h, or 4 =
(</span></font></span><font
size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial;
color:black'>the value of first burst shall not be settable by MODE =
SELECT).<span
style=3D"mso-spacerun: yes">&nbsp; </span>I&#8217;m sure we can resolve =
this at the SAS
protocol working group meeting next week.</span></font><font size=3D2
color=3Dblack face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial;
color:black;mso-color-alt:windowtext'><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'><![if =
!supportEmptyParas]>&nbsp;<![endif]></span></font><font
size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial;
color:black;mso-color-alt:windowtext'><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>Regards,</span></font><font =
size=3D2
color=3Dblack face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial;
color:black;mso-color-alt:windowtext'><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'><![if =
!supportEmptyParas]>&nbsp;<![endif]></span></font><font
size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial;
color:black;mso-color-alt:windowtext'><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>Mark Evans</span></font><font =
size=3D2
color=3Dblack face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial;
color:black;mso-color-alt:windowtext'><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>Maxtor =
Corporation</span></font><font
size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial;
color:black;mso-color-alt:windowtext'><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>408-894-5310</span></font><span
class=3DEmailStyle16><font size=3D2 color=3Dblack =
face=3DHelvetica><span
style=3D'font-size:10.0pt;mso-bidi-font-size:12.0pt;font-family:Helvetic=
a'><o:p></o:p></span></font></span></p>

<p class=3DMsoNormal><span class=3DEmailStyle16><font size=3D2 =
color=3Dblack
face=3DHelvetica><span =
style=3D'font-size:10.0pt;mso-bidi-font-size:12.0pt;
font-family:Helvetica'><![if =
!supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></span></font></span></p>=


<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DTahoma><span =
style=3D'font-size:
10.0pt;font-family:Tahoma;color:black'>-----Original Message-----<br>
<b><span style=3D'font-weight:bold'>From:</span></b> Nixon, Bob
[mailto:Bob.Nixon at emulex.com]<br>
<b><span style=3D'font-weight:bold'>Sent:</span></b> Tuesday, July 01, =
2003 9:14
AM<br>
<b><span style=3D'font-weight:bold'>To:</span></b> 'George Penokie'<br>
<b><span style=3D'font-weight:bold'>Cc:</span></b> t10 at t10.org<br>
<b><span style=3D'font-weight:bold'>Subject:</span></b> RE: A SAS =
Outstanding
Xfer_RDY Question.</span></font></p>

<p class=3DMsoNormal><font size=3D3 face=3D"Times New Roman"><span =
style=3D'font-size:
12.0pt'><![if =
!supportEmptyParas]>&nbsp;<![endif]><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D2 color=3Dblue face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:blue'>"...</span></font><font =
size=3D2
color=3Dblack face=3DArial><span =
style=3D'font-size:10.0pt;font-family:Arial;
color:black'>things will get ugly real quick but so be =
it..."</span></font><font
color=3Dblack><span =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>George, this is not an acceptable =
answer
for a commercial product.&nbsp; Given the current SAS =
standard:</span></font><font
color=3Dblack><span =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>1)&nbsp; There is no reason to =
expect
various initiators to coordinate setting of first =
burst.</span></font><font
color=3Dblack><span =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>2)&nbsp; In fact, this very issue =
will
lead them NOT to...each initiator may see some advantage (a hair better
performance, an increase in stability) to choosing their own value (or
zero)&nbsp;for first burst.</span></font><font color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>3 The result of my =
not&nbsp;designing for
noncoordinated settings is that MY initiator will hang.&nbsp; Doesn't =
matter
whose fault it is, in the eyes of the customer.&nbsp; In fact, if I =
don't
design for the worst case, it IS my fault.</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>4) Designing for the worst case =
as
pointed out&nbsp;earlier in this thread&nbsp;requires active assurance =
that the
setting of first burst is at least known before every comand is =
sent.&nbsp;
Since this involves awareness of unit attentions and sending of MODE
SENSE/SELECT commands, the transport layer becomes highly&nbsp;tangled =
with the
application.&nbsp; This was exactly what 02-403 was intended to =
untangle, but I
believe it didn't go far enough.</span></font><font color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>5)&nbsp; As Rob pointed out, I =
can't
simplify by forcing my own preferred value:&nbsp; I have to be able to =
detect
and support first burst of whatever current&nbsp;size in order to =
change first
burst to my preferred size.</span></font><font color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>6)&nbsp; SPC-3 hints =
that&nbsp;using
first burst of zero to disable first burst&nbsp;is an unacceptable
solution...in the specification of the first burst field it says =
"SCSI
transport protocols supporting this field shall provide an additional =
mechanism
to enable and disable the first burst function."&nbsp; Additional =
to
what?&nbsp; The only reasonable interpretation of the adjective
"additional" in this context is "other than the mode =
page
setting".&nbsp; SAS does not provide such an additional mechanism, =
so I
would claim it is out of compliance with SPC-3.</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>7)&nbsp; FCP-2 provides an
"additional mechanism" as a flag during login.&nbsp; Then
the&nbsp;PLDA&nbsp;interoperability&nbsp;profile requires that flag to =
be set
so as to prohibit using first burst at all.&nbsp; Given the above, =
this&nbsp;is
no surprise, and the precedent should be considered carefully by =
SAS.&nbsp; The
major vendors of FCP equipment still are able to demonstrate 99%+ of
theoretical performance, so the value-add of the first burst =
feature&nbsp;is
highly suspect.</span></font><font color=3Dblack><span =
style=3D'color:black;
mso-color-alt:windowtext'><o:p></o:p></span></font></p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>Taking all that into =
consideration, my
company and I would strongly recommend that one of the following =
resolutions be
incorporated in SAS 1.1 (in our preference order):</span></font><font
color=3Dblack><span =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>1)&nbsp; Obsolete first =
burst.</span></font><font
color=3Dblack><span =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>2)&nbsp; Provide a true =
"additional
mechanism" to disable it on a per initiator basis.&nbsp; Our =
proposal to
do it with a flag in the COMMAND IU is one such =
mechanism.</span></font><font
color=3Dblack><span =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>3)&nbsp; Make first burst a fixed =
value
by standard (e.g., "the value of first burst shall be =
10000h").</span></font><font
color=3Dblack><span =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>4)&nbsp; As a marginally =
acceptable
resolution, make first burst a fixed property of the target (i.e., =
"the
value of first burst shall not be settable by MODE =
SELECT).</span></font><font
color=3Dblack><span =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D2 color=3Dblack face=3DArial><span =
style=3D'font-size:
10.0pt;font-family:Arial;color:black'>&nbsp;&nbsp; - =
Bob</span></font><font
color=3Dblack><span =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal><font size=3D3 color=3Dblack face=3D"Times New =
Roman"><span
style=3D'font-size:12.0pt;color:black'>&nbsp;</span></font><font =
color=3Dblack><span
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>

<p class=3DMsoNormal style=3D'margin-bottom:12.0pt'><font size=3D2 =
color=3Dblack
face=3DTahoma><span =
style=3D'font-size:10.0pt;font-family:Tahoma;color:black'>-----Original
Message-----<br>
<b><span style=3D'font-weight:bold'>From:</span></b> George Penokie
[mailto:gop at us.ibm.com]<br>
<b><span style=3D'font-weight:bold'>Sent:</span></b> Tuesday, July 01, =
2003 6:24
AM<br>
<b><span style=3D'font-weight:bold'>To:</span></b> Nixon, Bob<br>
<b><span style=3D'font-weight:bold'>Cc:</span></b> t10 at t10.org<br>
<b><span style=3D'font-weight:bold'>Subject:</span></b> RE: A SAS =
Outstanding
Xfer_RDY Question.</span></font><font color=3Dblack><span =
style=3D'color:black;
mso-color-alt:windowtext'><o:p></o:p></span></font></p>

<p class=3DMsoNormal style=3D'margin-bottom:12.0pt'><font size=3D3 =
color=3Dblack
face=3D"Times New Roman"><span =
style=3D'font-size:12.0pt;color:black'><br>
</span></font><font size=3D2 color=3Dblack face=3Dsans-serif><span =
style=3D'font-size:
10.0pt;font-family:sans-serif;color:black'>Bob,</span></font><font =
color=3Dblack><span
style=3D'color:black'> <br>
<br>
</span></font><font size=3D2 color=3Dblack face=3Dsans-serif><span =
style=3D'font-size:
10.0pt;font-family:sans-serif;color:black'>A value of zero in the first =
burst
size field in the disconnect/reconnected mode page turns off first =
burst. There
is no need for any other mechanism. If initiators start making changes =
to mode
pages without cooperation from other initiators things will get ugly =
real quick
but so be it, that's the way mode pages work and have always worked. =
There are
many examples of this with first burst only being one. I believe the =
way it is
defined is just fine and that adding anything to the command to turn it =
on/off
would only add complexity with no added practical value.<br>
<br>
Bye for now,<br>
George Penokie<br>
<br>
Dept 2C6 &nbsp;114-2 N212<br>
E-Mail: &nbsp; &nbsp;gop at us.ibm.com<br>
Internal: &nbsp;553-5208<br>
External: 507-253-5208 &nbsp; FAX: 507-253-2880<br>
<br>
</span></font><font color=3Dblack><span style=3D'color:black'><br =
style=3D'mso-special-character:
line-break'>
<![if !supportLineBreakNewLine]><br =
style=3D'mso-special-character:line-break'>
<![endif]></span></font><font color=3Dblack><span =
style=3D'color:black;mso-color-alt:
windowtext'><o:p></o:p></span></font></p>

<table border=3D0 cellspacing=3D3 cellpadding=3D0 width=3D"100%" =
style=3D'width:100.0%;
 mso-cellspacing:1.5pt'>
 <tr>
  <td valign=3Dtop style=3D'padding:.75pt .75pt .75pt .75pt'>
  <p class=3DMsoNormal><![if !supportEmptyParas]>&nbsp;<![endif]><font =
size=3D3
  color=3Dblack face=3D"Times New Roman"><span =
style=3D'font-size:12.0pt;color:black;
  mso-color-alt:windowtext'><o:p></o:p></span></font></p>
  </td>
  <td valign=3Dtop style=3D'padding:.75pt .75pt .75pt .75pt'>
  <p class=3DMsoNormal><b><font size=3D1 color=3Dblack =
face=3Dsans-serif><span
  =
style=3D'font-size:7.5pt;font-family:sans-serif;color:black;font-weight:=
bold'>"Nixon,
  Bob" <Bob.Nixon at emulex.com&gt;</span></font></b><font =
color=3Dblack><span
  style=3D'color:black'> <br>
  </span></font><font size=3D1 color=3Dblack face=3Dsans-serif><span
  style=3D'font-size:7.5pt;font-family:sans-serif;color:black'>Sent by:
  owner-t10 at t10.org</span></font><font color=3Dblack><span =
style=3D'color:black'> </span></font><font
  color=3Dblack><span =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>
  <p><font size=3D1 color=3Dblack face=3Dsans-serif><span =
style=3D'font-size:7.5pt;
  font-family:sans-serif;color:black'>06/30/2003 03:51 =
PM</span></font><font
  color=3Dblack><span style=3D'color:black'> </span></font><font =
color=3Dblack><span
  =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>
  </td>
  <td valign=3Dtop style=3D'padding:.75pt .75pt .75pt .75pt'>
  <p class=3DMsoNormal><font size=3D1 color=3Dblack face=3DArial><span
  style=3D'font-size:7.5pt;font-family:Arial;color:black'>&nbsp; &nbsp; =
&nbsp;
  &nbsp; </span></font><font color=3Dblack><span =
style=3D'color:black'><br>
  </span></font><font size=3D1 color=3Dblack face=3Dsans-serif><span
  style=3D'font-size:7.5pt;font-family:sans-serif;color:black'>&nbsp; =
&nbsp; &nbsp;
  &nbsp; To: &nbsp; &nbsp; &nbsp; &nbsp;t10 at t10.org</span></font><font
  color=3Dblack><span style=3D'color:black'> <br>
  </span></font><font size=3D1 color=3Dblack face=3Dsans-serif><span
  style=3D'font-size:7.5pt;font-family:sans-serif;color:black'>&nbsp; =
&nbsp; &nbsp;
  &nbsp; cc: &nbsp; &nbsp; &nbsp; &nbsp;</span></font><font =
color=3Dblack><span
  style=3D'color:black'> <br>
  </span></font><font size=3D1 color=3Dblack face=3Dsans-serif><span
  style=3D'font-size:7.5pt;font-family:sans-serif;color:black'>&nbsp; =
&nbsp; &nbsp;
  &nbsp; Subject: &nbsp; &nbsp; &nbsp; &nbsp;RE: A SAS Outstanding =
Xfer_RDY
  Question.</span></font><font color=3Dblack><span =
style=3D'color:black'> </span></font><font
  color=3Dblack><span =
style=3D'color:black;mso-color-alt:windowtext'><o:p></o:p></span></font>=
</p>
  </td>
 </tr>
</table>

<p class=3DMsoNormal style=3D'margin-bottom:12.0pt'><font size=3D3 =
color=3Dblack
face=3D"Times New Roman"><span =
style=3D'font-size:12.0pt;color:black'><br>
<br>
<br>
</span></font><font size=3D2 color=3Dblack face=3D"Courier New"><span
style=3D'font-size:10.0pt;font-family:"Courier New";color:black'>* From =
the T10
Reflector (t10 at t10.org), posted by:<br>
* "Nixon, Bob" <Bob.Nixon at Emulex.Com&gt;<br>
*<br>
How does an initiator indicate to a target whether to use first burst =
or<br>
not? &nbsp;<br>
<br>
Both SAM-3 and SAS specify that the Send SCSI Command and SCSI =
Command<br>
Received transport services include a parameter indicating whether =
first<br>
burst is enabled or not. &nbsp;The prior discussion in this thread =
makes it<br>
obvious the choice of the initiator has to be communicated to the =
target in<br>
order that XFER_RDY can be sent when needed.<br>
<br>
We could claim setting the first burst size to zero in the<br>
disconnect-reconnect mode page accomplishes the necessary =
communication.<br>
But this would lead to possibly disastrous inefficiency...the first =
burst<br>
size setting affects all initiators for a port and can be changed by =
any of<br>
them at any time. &nbsp;Every initiator would have to assure the =
correct mode<br>
page setting before every command. &nbsp;The means of doing this are =
messy at<br>
best.<br>
<br>
FCP-2 is the only other protocol that I could find that supports =
first<br>
burst. &nbsp;It implements the required means to disable first burst by =
a<br>
per-initiator login flag (though this falls a little short of the<br>
per-command implication of the transport service specification in =
SAM-3).
&nbsp;I<br>
would recommend SAS 1.1 meet the requirement by adding a bit to the =
SSP<br>
COMMAND IU indicating whether the target is to honor (bit=3D0) or =
ignore<br>
(bit=3D1) first burst size for the command.<br>
<br>
I'll write this up for next week unless one of you educates me before =
then.<br>
<br>
<br>
&nbsp; - Bob<br>
<br>
-----Original Message-----<br>
From: Evans, Mark [mailto:Mark_Evans at maxtor.com]<br>
Sent: Friday, June 27, 2003 2:29 PM<br>
To: 'Sheffield, Robert L'; t10 at t10.org<br>
Subject: RE: A SAS Outstanding Xfer_RDY Question.<br>
<br>
<br>
* From the T10 Reflector (t10 at t10.org), posted by:<br>
* "Evans, Mark" <Mark_Evans at maxtor.com&gt;<br>
*<br>
Hi Bob,<br>
<br>
If the value in the FIRST BURST SIZE field is not zero, all of the =
rules for<br>
first burst are the same as for an XFER_RDY, that is, a SAS target =
port<br>
shall not send an XFER_RDY until all of the data for the first burst =
has<br>
been sent. &nbsp;This is explicit in the standard in 10.2.6.1.5 FIRST =
BURST
SIZE<br>
field. &nbsp;The following is the fourth paragraph in that clause:<br>
<br>
"If the amount of data to be transferred for the command is less =
than the<br>
amount of data specified by the FIRST BURST SIZE field, the SSP target =
port<br>
shall not transmit an XFER_RDY frame for the command. &nbsp;If the =
amount of
data<br>
to be transferred for the command is greater than the amount of =
data<br>
specified by the FIRST BURST SIZE field, the SSP target port shall =
transmit<br>
an XFER_RDY frame after it has received all of the data specified by =
the<br>
FIRST BURST SIZE field from the initiator. &nbsp;All data for the =
command is
not<br>
required to be transferred during the same connection in which the =
command<br>
is transferred."<br>
<br>
I guess we could make this stronger by changing, "...the SSP =
target port<br>
shall transmit an XFER_RDY frame after it has received all of the =
data<br>
specified by the FIRST BURST SIZE field..." to "...the SSP =
target
port shall<br>
not transmit an XFER_RDY frame until it has received all of the =
data<br>
specified by the FIRST BURST SIZE field...", but the first was =
intended to<br>
mean the second.<br>
<br>
Regards,<br>
<br>
Mark Evans<br>
Maxtor Corporation<br>
<br>
-----Original Message-----<br>
From: &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;Sheffield,
Robert L [mailto:robert.l.sheffield at intel.com] <br>
Sent: &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; Friday, =
June 27,
2003 12:44 PM<br>
To: &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
t10 at t10.org<br>
Subject: &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; RE: A =
SAS
Outstanding Xfer_RDY Question.<br>
<br>
* From the T10 Reflector (t10 at t10.org), posted by:<br>
* "Sheffield, Robert L" =
<robert.l.sheffield at intel.com&gt;<br>
*<br>
I didn't see this the last time I looked into the question, but it does =
look<br>
like only one XFER_RDY can be outstanding at a time. I looked into it =
before<br>
because of a question about the first burst transfer, and what sort =
of<br>
timeout might occur in case the first burst never completes. I assumed =
that<br>
since the first burst is an implicit XFER_RDY, that the timeout would =
be the<br>
same whether it's the first burst or a transfer associated with an =
explicit<br>
XFER_RDY (the Initiator Response Timeout timer). What I'm left =
wondering now<br>
is if the target must wait for the first burst transfer to complete =
before<br>
sending the first XFER_RDY? Is that the intent, and is is stated =
anywhere?<br>
<br>
Bob Sheffield<br>
<br>
-----Original Message-----<br>
From: Sriram Srinivasan [mailto:srirams at lsil.com]<br>
Sent: Friday, June 27, 2003 11:31 AM<br>
To: t10 at t10.org</span></font><font color=3Dblack><span =
style=3D'color:black'> <br>
</span></font><font size=3D2 color=3Dblack face=3D"Courier New"><span
style=3D'font-size:10.0pt;font-family:"Courier =
New";color:black'>Subject: RE: A
SAS Outstanding Xfer_RDY Question.<br>
<br>
<br>
* From the T10 Reflector (t10 at t10.org), posted by:<br>
* Sriram Srinivasan <srirams at lsil.com&gt;<br>
*<br>
<br>
&nbsp;If sas-r04a.pdf is the current SAS spec, I see that in =
"10.2.1.8
Receive <br>
Data-Out transport protocol service" it talks about limiting =
number of <br>
outstanding XFER_RDY frames per command to 1. &nbsp;I don't see where =
it allows
<br>
more than 1 outstanding XFER_RDY frame per command.<br>
&nbsp;<br>
&nbsp;<br>
&nbsp;\Sriram\<br>
&nbsp;<br>
" <br>
" * From the T10 Reflector (t10 at t10.org), posted by:<br>
" * "Bill Galloway" <BillG at breatech.com&gt;<br>
" *<br>
" I believe the current SAS spec allows more than one outstanding =
XFER_RDY
<br>
per<br>
" command. &nbsp;There was some talk of limiting this but it never =
went
anywhere.<br>
" <br>
" Bill Galloway<br>
" Pivot3, Inc.<br>
" BillG at pivot3.com<br>
" P: (281) 530-3063<br>
" F: (281) 988-0398 <br>
" <br>
" -----Original Message-----<br>
" From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of
Whitehill,<br>
" Cliff<br>
" Sent: Friday, June 27, 2003 11:03 AM<br>
" To: t10 at t10.org<br>
" Subject: A SAS Outstanding Xfer_RDY Question.<br>
" <br>
" <br>
" * From the T10 Reflector (t10 at t10.org), posted by:<br>
" * "Whitehill, Cliff" <cwhitehi at lsil.com&gt;<br>
" *<br>
" All,<br>
" <br>
" My current understanding is that for SAS you can have only one
outstanding<br>
" Xfer_RDY per command. &nbsp;Is this true? If so, where does it =
say this
in the<br>
" SAS specification?<br>
" <br>
" Regards,<br>
" <br>
" --------------------------------------------<br>
" Clifford A. Whitehill<br>
" Staff Systems Engineer<br>
" LSI Logic Corp.<br>
" 2001 Danfield Ct.<br>
" Fort Collins, CO. 80525<br>
" Tel: 970-206-5024<br>
" Fax: 970-206-5244<br>
" email: cliff.whitehill at lsil.com<br>
" <br>
" *<br>
" * For T10 Reflector information, send a message with<br>
" * 'info t10' (no quotes) in the message body to =
majordomo at t10.org<br>
" <br>
" *<br>
" * For T10 Reflector information, send a message with<br>
" * 'info t10' (no quotes) in the message body to =
majordomo at t10.org<br>
<br>
<br>
<br>
----------------------------------------------------------------------<b=
r>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; "FORGET =
NOT THAT
THE EARTH DELIGHTS TO FEEL YOUR BARE FEET,<br>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; AND THE WINDS LONG TO =
PLAY
WITH YOUR HAIR"<br>
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;-Khalil
Gibran<br>
<br>
Sriram Srinivasan &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;
&nbsp; &nbsp; &nbsp; Sriram.Srinivasan at lsil.com<br>
ASIC Design Engineer, LSI Logic,<br>
2001 Danfield Ct., &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; Phone: 970-206-5847<br>
Fort Collins, CO 80525 &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; =
&nbsp;
&nbsp; &nbsp; &nbsp; &nbsp;FAX &nbsp;: 970-206-5244<br>
----------------------------------------------------------------------<b=
r>
<br>
*<br>
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* 'info t10' (no quotes) in the message body to majordomo at t10.org<br>
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