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    RE: Framing Discussion



     
    > 
    > 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.
    
    No. Why do you need a copy ? These buffers are consumed
    by iscsi layer and may be returned later to the same
    pool. These are just some details.
    
    > 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.
    > 
    Why are they not interchangeable ? This is an
    assumption not stated anywhere.  Is there
    a list of other assumptions that is documented ?
    
    -mohan
    
    
      
    > --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 
    > > > 
    > 
    


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