SAS state machine overview

Elliott, Robert (Server Storage) elliott at hp.com
Tue Nov 30 17:23:40 PST 2004


* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Server Storage)" <elliott at hp.com>
*
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SATA was designed as a point-to-point, narrow-ported protocol, so it
assumed the transport layer and link layer were directly connected to
each other.  When one of the SAS link layers establishes an STP
connection, the SAS port layer is modeled as just connecting a single
SATA transport layer to a SATA link layer and then standing aside - =
SATA
then defines everything until the connection closes and the SAS link
layer and port layer step in again. Multiple STP connections between =
the
same initiator port and target port are not allowed.
=20
(See editor's note 2 discussing implications of SATA port multipliers =
on
the STP model, just after figure 29)
=20
SSP, on the other hand, supports more than one connection at a time =
from
a port. The SSP transport layer doesn't care how many connections are
currently open or about the identities of the SSP ports on the other =
end
of those connections. It spawns one "transport server" state machine =
per
tag, representing the concurrency of the outstanding commands.  For
incoming frames, the port layer funnels each frame (from any link layer
with an SSP connection) to a single SSP transport layer.  The "frame
router" state machine in the SSP transport layer then routes the frame
to the appropriate per-tag state machine.
=20
SMP is a mix; the port layer doesn't stand aside during the connection,
but there is one SMP transport layer per SMP link layer, working in
lockstep.  Multiple SMP connections between the same initiator port and
target port are allowed (but they run independently).  The SMP =
transport
layer and link layer only operate for the duration of the connection
(unlike SSP and STP, which allow disconnects).
=20
--=20
Rob Elliott, elliott at hp.com=20
Hewlett-Packard Industry Standard Server Storage Advanced Technology=20
https://ecardfile.com/id/RobElliott
<https://ecardfile.com/id/RobElliott> =20

=20


  _____ =20

From: Bill Martin [mailto:bill_martin at sierralogic.com]=20
Sent: Tuesday, November 30, 2004 4:16 PM
To: Elliott, Robert (Server Storage); t10 at t10.org
Subject: SAS state machine overview



Rob & T10 community:

=20

In looking at the overview of the SAS state machines in 4.3.1 of the =
SAS
draft, there is an implication that for STP and SMP multiple images of
this may be running concurrently; however, for SSP only one image is
supported.  Is this intentional, and if so why; or is this an oversight
in figure 29 on page 50 (pdf 84)?

=20

Thanks for any input on this.

=20

Bill Martin

Sr. Principal Engineer

Standards and Interoperability

Sierra Logic, Inc.

916 772-1234 x 112

bill_martin at sierralogic.com

=20


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<DIV dir=3Dltr align=3Dleft><SPAN class=3D465295600-01122004><FONT =
face=3DArial=20
color=3D#0000ff size=3D2>SATA was designed as a point-to-point,=20
narrow-ported&nbsp;protocol, so it assumed the transport layer and link =
layer=20
were directly connected to each other.&nbsp; <SPAN=20
class=3D465295600-01122004><FONT face=3DArial color=3D#0000ff =
size=3D2>When one of the=20
SAS link layers establishes an STP connection, the SAS port layer is =
modeled as=20
just connecting a single SATA transport layer to a SATA link layer and =
then=20
standing aside - SATA then defines everything until the connection =
closes and=20
the SAS link layer and port layer step in again. Multiple STP =
connections=20
between the same initiator port and target port are not=20
allowed.</FONT></SPAN></FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D465295600-01122004><FONT =
face=3DArial=20
color=3D#0000ff size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D465295600-01122004><SPAN=20
class=3D465295600-01122004><FONT face=3DArial color=3D#0000ff =
size=3D2>(See editor's=20
note 2 discussing implications of SATA port multipliers on the STP =
model, just=20
after figure 29)</FONT></SPAN></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D465295600-01122004><SPAN=20
class=3D465295600-01122004><FONT face=3DArial color=3D#0000ff=20
size=3D2></FONT></SPAN></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D465295600-01122004>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D465295600-01122004><FONT =
face=3DArial=20
color=3D#0000ff size=3D2>SSP, on the other hand, supports&nbsp;more =
than one=20
connection at a time&nbsp;from a port.&nbsp;The SSP transport layer =
doesn't care=20
how many&nbsp;connections are currently open or&nbsp;about the =
identities=20
of&nbsp;the SSP ports&nbsp;on the other end of those connections. It =
spawns one=20
"transport server" state machine per tag, representing the concurrency =
of the=20
outstanding commands.&nbsp; For incoming frames, the port layer funnels =
each=20
frame (from any link layer with an SSP connection) to a single=20
SSP&nbsp;transport layer.&nbsp; The "frame router" state machine in the =
SSP=20
transport layer then routes the frame to the appropriate per-tag state=20
machine.</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D465295600-01122004><FONT =
face=3DArial=20
color=3D#0000ff size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D465295600-01122004><FONT =
face=3DArial=20
color=3D#0000ff size=3D2>SMP is a mix; the port layer doesn't stand =
aside during the=20
connection, but there is one SMP transport layer per SMP link layer, =
working in=20
lockstep.&nbsp; Multiple SMP connections between the same initiator =
port and=20
target port are allowed (but they run independently).&nbsp; The SMP =
transport=20
layer and link layer only operate for the duration of the connection =
(unlike SSP=20
and STP, which allow disconnects).</FONT></SPAN></DIV>
<DIV dir=3Dltr align=3Dleft><SPAN class=3D465295600-01122004><FONT =
face=3DArial=20
color=3D#0000ff size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV dir=3Dltr align=3Dleft></SPAN><SPAN lang=3Den-us><FONT =
face=3DArial=20
size=3D2>--</FONT></SPAN> <BR><SPAN lang=3Den-us><FONT face=3DArial =
size=3D2>Rob=20
Elliott, elliott at hp.com</FONT></SPAN> <BR><SPAN lang=3Den-us><FONT =
face=3DArial=20
size=3D2>Hewlett-Packard Industry Standard Server Storage Advanced=20
Technology</FONT></SPAN> <BR><SPAN lang=3Den-us><FONT face=3DArial =
size=3D2><A=20
href=3D"https://ecardfile.com/id/RobElliott">https://ecardfile.com/id/Ro=
bElliott</FONT></SPAN>=20
</DIV></DIV><BR>
<DIV>&nbsp;</DIV><BR>
<BLOCKQUOTE dir=3Dltr=20
style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px =
solid; MARGIN-RIGHT: 0px">
  <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, =
November 30,=20
  2004 4:16 PM<BR><B>To:</B> Elliott, Robert (Server Storage);=20
  t10 at t10.org<BR><B>Subject:</B> SAS state machine =
overview<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">Rob &amp; T10=20
  community:<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">In looking at the =
overview of the=20
  SAS state machines in 4.3.1 of the SAS draft, there is an implication =
that for=20
  STP and SMP multiple images of this may be running concurrently; =
however, for=20
  SSP only one image is supported. &nbsp;Is this intentional, and if so =
why; or=20
  is this an oversight in figure 29 on page 50 (pdf=20
  84)?<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 input on =

  this.<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">Bill=20
  Martin<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">Sr. Principal=20
  Engineer</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">Standards and=20
  Interoperability</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">Sierra Logic,=20
  Inc.<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">916 772-1234 x=20
  112<o:p></o:p></SPAN></FONT></P>
  <P class=3DMsoNormal><U1:PERSONNAME u2:st=3D"on"><FONT face=3DArial =
size=3D2><SPAN=20
  style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial">bill_martin at sierralogic.com</SPAN></FONT></U1:PERSONNAME><FONT=20
  face=3DArial size=3D2><SPAN=20
  style=3D"FONT-SIZE: 10pt; FONT-FAMILY: =
Arial"><o:p></o:p></SPAN></FONT></P>
  <P class=3DMsoNormal><FONT face=3D"Times New Roman" size=3D3><SPAN=20
  style=3D"FONT-SIZE: =
12pt"><o:p>&nbsp;</o:p></SPAN></FONT></P></DIV></BLOCKQUOTE></BODY></HTM=
L>

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