RE: Framing Discussion

[Black_David@emc.com]

This issue is one of how SCSI interfaces to the
operating system.  Operating systems issue a
SCSI read and provide a buffer (e.g., a page
from the file buffer cache or the like) into
which the data is to be read.  SCSI and Fibre
Channel HBAs are capable of taking the data
directly off the bus/cable/wire/fiber and putting
it into exactly the right place in the correct
buffer.  The approach Mohan outlines below reads
the data into some buffer and then has to copy
it into the right place when parsing of the
iSCSI header(s) reveals what that place is.
The design goal behind the framing discussion
is avoidance of that copy.  In contrast to the
typical case for NICs and TCP/IP, read data
buffers for SCSI data are usually *not*
interchangeable.

--David
---------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
+1 (508) 435-1000 x75140     FAX: +1 (508) 497-8500
black_david@emc.com       Mobile: +1 (978) 394-7754
---------------------------------------------------

> -----Original Message-----
> From:	Mohan Parthasarathy [SMTP:Mohan.Parthasarathy@eng.sun.com]
> Sent:	Tuesday, December 19, 2000 6:06 PM
> To:	ips@ece.cmu.edu; marjorie_krueger@hp.com
> Subject:	Re: Framing Discussion
> 
> Hi Marjorie,
> 
> The section on "How can we accomplish direct data placement",
> seems to assume that there is a separate buffer allocated
> by the iscsi layer to receive the data from the network.
> Is this an implicit assumption on how iscsi will be built ?
> 
> I can see iscsi layer sitting on top of TCP posting iscsi
> commands, and receiving buffers from the network as they
> come. Assume the NIC has a pool of buffers for the
> iscsi connection. When the data comes from the network, i
> can assume that the NIC is able to parse the TCP/IP headers
> and locate the right buffer pool for receiving data. As the
> data is received, it can be returned to the iscsi layer
> which can interpret the iscsi header and the length and hence
> the data following the iscsi header and also more iscsi headers
> that follow it. In this model, i don't see any difficulty
> in data placement unless i am missing something.
> 
> -mohan
> 
> > From owner-ips@ece.cmu.edu Tue Dec 19 11:12:06 2000
> > X-Authentication-Warning: ece.cmu.edu: majordom set sender to
> owner-ips@ece.cmu.edu using -f
> > From: "KRUEGER,MARJORIE (HP-Roseville,ex1)" <marjorie_krueger@hp.com>
> > To: "Ips Reflector (E-mail)" <ips@ece.cmu.edu>
> > Subject: Framing Discussion
> > Date: Tue, 19 Dec 2000 10:08:05 -0700
> > MIME-Version: 1.0
> > 
> > Attached are the minutes of the technical meeting to discuss framing
> held
> > 11/29/2000 in San Jose, CA.  I created it with Acrobat 4.0, a free
> reader
> > can be installed from
> http://www.adobe.com/products/acrobat/readstep2.html
> > 
> > This document contains the mathmatical support for the general feeling
> that
> > we won't be able to do > 1 Gbps over TCP without some framing help.
> > 
> > Marjorie Krueger
> > Networked Storage Architecture
> > Networked Storage Solutions Org.
> > Hewlett-Packard
> > tel: +1 916 785 2656
> > fax: +1 916 785 0391
> > email: marjorie_krueger@hp.com 
> >