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RE: iscsi: 08 Comment, framing
Julian is
correct. In London the framing team consensus did not
translate
into WG rough consensus. Until it does, I think
modifications
to the spec
are not appropriate. I suspect Framing is going to be
on
the Salt
Lake City agenda :-(. --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 ---------------------------------------------------
Dave,
This was the
consensus of the framing team - not of the IPS list. It is inappropriate for us to replace a thing that we
have and is agreed to something that that is not here yet.
As I stated if you want to do it independent of the ULP progress you
have to reopen the issue on this list.
Regards, Julo
| Dave Sheehy
<dbs@acropora.rose.agilent.com> Sent by: owner-ips@ece.cmu.edu
09-10-01 08:54 Please respond to Dave Sheehy
| To:
ips@ece.cmu.edu (IETF IP SAN Reflector) cc:
Subject: iscsi: 08 Comment,
framing
|
Since the following is the consensus of the framing team:
>
iSCSI, with minor modifications since the presentation at the IETF: >
> >
The Sender: >
- MUST
support no framing >
- MUST
support at least one framing solution >
- MUST use the framing specified by the receiver, >
if it supports that framing mode
and
...
> > First, a quick summary of the issues: >
- Deploying iSCSI
sender can be done: >
- on top
of an unmodified TCP stack with: >
o No
framing >
o Marker based framing >
- on top of a modified TCP stack can
implement >
PDU-alignment. >
- The receiver
trade-offs are: >
o No
framing - large receive reassembly buffer >
(higher cost solution) >
o
Marker framing - receive reassembly buffer is reduced >
to an eddy buffer, but requires modifications to > >
TCP receive stack (medium cost solution) >
o PDU-alignment - receive reassembly
buffer can be > reduced >
even
further, but requires modifications to TCP >
receive stack (lowest cost solution and enables >
eventual deployment of a viable chunking protocol). >
- The cost of
implementing markers on unmodified TCP stacks >
o sender cost is acceptable, assuming a gather list
is >
reasonably implemented. >
o receiver cost is
unacceptable
> Initial implementations for initiator appear to be in
two camps: >
- Unmodified TCP software stacks >
- Embedded TCP offload in the NIC
(essentially TCP >
is
hidden from the host SCSI stack) > > Initial implementations for
the target appear to be in two camps: >
- Optimized NICs which will support framing
- probably both >
framing
modes. Because both modes >
require modifications to the receive TCP stack and >
PDU-alignment is viewed as straightforward, it is
>
assumed that most
implementations will implement >
both framing solutions to allow them to transfer >
data optimally with either unmodified send TCP
stacks >
or PDU-alignment send
TCP stacks. >
- Unmodified TCP software stacks > > It is primarily a
receiver cost issue that motivates the framing > discussion. The primary
sender issue is what, if any, optimizations can > be done for unmodified
TCP send stacks? Note however, that the proposed > iSCSI requirements
are not target or initiator oriented - they are > sender and receiver
oriented. The receiver cost issue applies to either > a target or
initiator - and they each have very different cost > trade-offs.
> > Thus the best solution is to allow the receive side to
control their > destiny - and require the sender to obey the receiver
(within limits). > If this approach were taken, the sender would have to
implement all > three framing options. Unfortunately, a highly desirable
design goal is > to allow the sender (either the target or the
initiator) to run on an > unmodified TCP stack. Thus the compromise in
terms of sender > functionality.
The iSCSI 08 draft Appendix C
MUST be amended,
from,
"The use of markers is negotiable. The
initiator and target MAY indicate their readiness to receive and/or send
markers during login separately for each connection. The default is NO. In
certain environments a sender not willing to supply markers to a
receiver willing to accept markers MAY suffer from a considerable
performance degradation."
to:
"The use of markers is negotiable. The
initiator and target MUST indicate their readiness to receive and/or send
markers during login separately for each connection. The default is NO. In
certain environments a sender not willing to supply markers to a
receiver willing to accept markers MAY suffer from a considerable
performance degradation."
and in the next paragraph:
"If a
receiver indicates that it desires a marker, the sender SHOULD agree
(during negotiation) and provide the marker at the desired
interval."
MUST be changed to:
"If a receiver indicates that it
desires a marker, the sender MUST agree (during negotiation) and provide
the marker at the desired interval."
Dave
Sheehy
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