[7203] in linux-scsi channel archive
Re: Fixing SCSI Layer
daemon@ATHENA.MIT.EDU (Tony Chung)
Fri Sep 10 16:05:30 1999
Date: Fri, 10 Sep 1999 12:52:43 -0700
From: Tony Chung <chungto@ampex.com>
To: Gerard Roudier <groudier@club-internet.fr>
CC: linux-scsi@vger.rutgers.edu
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Gerard Roudier wrote:
>
>
> UDI is not a standard and seem to me some poor sci-fi and will never
> happen in my systems.
I just browse http://www.projectudi.org/ and find out that Intel already
porting UDI in Linux as proof of concept.
> CAM requires the data direction (or none) to be provided in the Execute
> SCSI IO request CCB, but existing Linux applications donnot provide the
> data direction since the current SCSI interface just does not allow this
> information to be passed. We must deal with compatibility issues.
Current linux-scsi:
(High level drivers eg. sd, st) <--> (middle layer) <---> (
host adaptor layer)
Future layers:
(Old drivers) <----> (middle layer *) <---(UDI SCSI layer)
<---> (old host adaptor layer)
^--------------------------------^
(New perihperal drivers) <------------- >(UDI SCSI layer) <--->
(new UDI host adaptor drivers)
With multiple paths, you can maintain backward binary compatible and user still can
pick the fastest path for efficiency.
If old drivers do not pass DATA_DIRECTION, then the middle layer can figure it out
and pass it
to the UDI SCSI layer and take advantages of latest hardware. If not, they have to
write their own
perihperal drivers.
>
>
>
> The better one is the one that is a real standard. The other one is to be
> ignored, in my opinion.
You may want to look at UDI more carefully because:
1. support by major vendors like Sun, HP, IBM and Compaq (which buyout DEC and
abandon CAM).
2. Intel is porting UDI for Linux now!
3. UDI support SCSI-3 (including Fibre Channel)...Do CAM support that?
>
>
> Gérard.
--
=============================
Tony Chung
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Gerard Roudier wrote:
<blockquote TYPE=CITE>
<p>UDI is not a standard and seem to me some poor sci-fi and will never
<br>happen in my systems.</blockquote>
I just browse <A HREF="http://www.projectudi.org/">http://www.projectudi.org/</A> and find out that Intel already
<br>porting UDI in Linux as proof of concept.
<br>
<blockquote TYPE=CITE>CAM requires the data direction (or none) to be provided
in the Execute
<br>SCSI IO request CCB, but existing Linux applications donnot provide
the
<br>data direction since the current SCSI interface just does not allow
this
<br>information to be passed. We must deal with compatibility issues.</blockquote>
Current linux-scsi:
<br>
(High level drivers eg. sd, st) <--> (middle layer) <--->
( host adaptor layer)
<p>Future layers:
<br>
<br>
(Old drivers) <----> (middle layer *) <---(UDI
SCSI layer) <---> (old host adaptor layer)
<br>
^--------------------------------^
<br>
(New perihperal drivers) <------------- >(UDI SCSI layer)
<---> (new UDI host adaptor drivers)
<p>With multiple paths, you can maintain backward binary compatible and
user still can
<br>pick the fastest path for efficiency.
<br>If old drivers do not pass DATA_DIRECTION, then the middle layer can
figure it out and pass it
<br>to the UDI SCSI layer and take advantages of latest hardware.
If not, they have to write their own
<br>perihperal drivers.
<blockquote TYPE=CITE>
<br>
<p>The better one is the one that is a real standard. The other one is
to be
<br>ignored, in my opinion.</blockquote>
You may want to look at UDI more carefully because:
<br>1. support by major vendors like Sun, HP, IBM and Compaq (which buyout
DEC and abandon CAM).
<br>2. Intel is porting UDI for Linux now!
<br>3. UDI support SCSI-3 (including Fibre Channel)...Do CAM support
that?
<blockquote TYPE=CITE>
<p>Gérard.</blockquote>
<pre>--
=============================
Tony Chung</pre>
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