RE: iSCSI: Framing Steps

["Shah, Hemal" <hemal.shah@intel.com>]

David,

I agree with your conclusions. I would like to add something
related to framing. Framing by itself solves only part of the
problem from the perspective of sync and steering. I am not going
to summarize pro/cons of each framing proposal here as they have
been summarized in the previously posted emails.

I would add though that all different forms of framing proposals
put some sort of aritificial limitation on max. iSCSI PDU size
- TUF requires an iSCSI PDU to be contained within Framing PDU
- FIM & COWS require iSCSI PDU reassembly buffer in case of a
  packet loss (Thus, amount of buffering on NIC/HBA dictates max.
  iSCSI PDU size)

In addition to framing, you definitely need some sort of steering
mechanism that completely eliminates reassembly buffers on NIC
and does not put any artificial limitation on Max. iSCSI PDU size.
If this steering layer is generic (DDP/RDMA), then the NIC/HBA
now has wider applicability.

In my opinion, until sync and steering layers related issues are
resolved, framing/DDP/RDMA are premature at this point to be
included in iSCSI 1.0 draft.

Hemal


-----Original Message-----
From: Black_David@emc.com [mailto:Black_David@emc.com]
Sent: Thursday, January 24, 2002 1:10 AM
To: ips@ece.cmu.edu
Subject: iSCSI: Framing Steps


I want to attempt to make some steps towards resolving
the framing issues.  In reviewing the recent discussions
on framing, I have a couple of conclusions:

(1) I do not believe that WG consensus (rough or otherwise)
	can be obtained for a "MUST implement" requirement
	for any form of framing.
(2) The COWS mechanism has a lot of potential, but
	its newness, the multiple versions that
	have been mentioned, and the desire for some
	sort of alignment with new work on DDP/RDMA
	suggest that COWS is premature to specify as
	part of iSCSI.

I suggest that these conclusions form the
basis for further ips WG consideration of framing.

Please think carefully before objecting to these
conclusions on the list (I'm happy to respond to
private questions/expressions of concern).  If the
framing issue cannot be driven to closure in
the next few weeks, I will be forced to conclude
that the entire topic is experimental, and hence
needs to be removed from the iSCSI specification
and handled in separate drafts intended to become
experimental RFCs.

Thanks,
--David

p.s. A desire to build NICs that never behave in
accordance with an important SHOULD in RFC 1122
(out-of-order segments SHOULD be queued) does not
strike me as a good reason for changing the first
conclusion above.

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