RE: iSCSI: Flow Control

[Jim McGrath <Jim.McGrath@quantum.com>]

BTW, on the issue of adjusting the total amount of RAM available to allow us
to avoid the protocol issue, this will not work for moderately priced NAS
boxes.  These are focused on ease of use, and so are sealed and not end user
(or channel) configurable.  Off the top of my head I'd estimate that
approach would not work for NAS devices selling for $10,000 or less - any
perhaps not very well for those selling for several tens of thousands of
dollars.

Even if the boxes are technically capable of accepting more RAM, the
configuration you want depends on the deployment - which is determined by
the end user, and may be changed through subsequent redeployment.  For a
traditional heavy touch IS operation that is fine, but not for those working
outside the glass house.  This is not to say there will not be different
amounts of buffering used - a 1 disk NAS will have less than a 10 disk NAS.
But no one I knows wants to produce multiple versions of 4 disk NAS, with
differing amounts of buffering, if they can avoid it.

Jim

PS of course, if the focus of iSCSI was just the machine room then this
becomes manageable, but that is not what I am hearing people talk about.



-----Original Message-----
From: Jim McGrath 
Sent: Wednesday, October 04, 2000 7:37 PM
To: 'John Hufferd/San Jose/IBM'; IPS@ece.cmu.edu
Subject: RE: iSCSI: Flow Control



I agree that there is a difference in the degree of buffer requirements
based on true internet vs machine room application.  However, I don't think
vendors will necessarily design their products differently for the two
applications.  And even in a machine room setting (e.g. today's parallel
SCSI and Fibre Channel), people have requested immediate data on writes
(which is what this feature is designed to provide).

I don't think leaving this out of the iSCSI protocol is wise - we have
already had a market failure (i.e. an experience where a desired feature
could not be supported by the vendors) in this area with Fibre Channel, and
it just looks worse going forward.  I fear coupling to sessions sounds too
much like coupling to login, which did not work in FC-AL.

BTW, the burden here is almost entirely on the target.  The target is the
one responsible for allocating the buffers - the hosts just have to respond
to changes in the amount available.  Unless this is really hard for the host
to do(?)

Jim


-----Original Message-----
From: John Hufferd/San Jose/IBM [mailto:hufferd@us.ibm.com]
Sent: Wednesday, October 04, 2000 2:58 PM
To: IPS@ece.cmu.edu
Subject: RE: iSCSI: Flow Control



OK,
I can buy that Peer to Peer Session stuff.  So we, at least we seem to be
in agreement on these items. (The length of "normal" Sessions, the length
of Peer to Peer Sessions, and the Dynamic Buffering requirements for
Storage Controllers.)

So let me push this slightly.  I also believe that when Storage Controllers
are sold as iSCSI Internet (by that I mean long distance connect) capable,
there will be a RAM Storage Feature that is recommended by the Vendor.  Any
one that just wants to use the Storage Controller in areas where SCSI Buss
or FC distances apply today, might not need the additional RAM feature.

I think that is the way this stuff will be sold (and need to be sold) and
vendors will then compete on their more optimum ways of using the RAM
buffers.

There may be a variant of the above where the Vendor Sells the RAM Storage
Feature based on the number of Concurrent Sessions the customers wants to
sustain.  And of course there will be combinations of RAM Storage Features
for number of Sessions and Distance.  Vendors will compete on how simple
(in relationship to Cost and performance) their approach is viewed relative
to the Distance and number of Sessions needed.

If others believe this, then the stuff we have been talking about with
regards to  Flow Control is Mute and can be left up to TCP/IP and the
various vendors implementations of the iSCSI/SCSI buffering algorithms.

.
.
.
John L. Hufferd


Michael Krause <krause@cup.hp.com>@ece.cmu.edu on 10/04/2000 01:44:25 PM

Sent by:  owner-ips@ece.cmu.edu


To:   IPS@ece.cmu.edu
cc:
Subject:  RE: iSCSI: Flow Control



At 12:34 PM 10/4/00 -0700, John Hufferd/San Jose/IBM wrote:

>Michael Krause,
>First, a session usually lasts from Boot Time till it is Booted again or
>stopped.  The variant to this is a Storage Device being used in a manor
>like a Mount or Map done with NAS.  Even then, most folks, have that setup
>so the Mounting and Mapping is done at bring up, though it is sometimes
>done at other times, but even then it is left around.  So I think the
thing
>you can say about Session Time as the term is used in the iSCSI context is
>that it is LONG.
>
>I do not think we have consensus about the notification of available
>buffers.  With the way many systems work, is (as stated above), all
devices
>are set up at startup of the Host, and the Session is kept around by the
>Host, even if there hasn't been anything which use that device all
>day/week, etc.  So I am not sure if having a certain amount of buffer
space
>reserved for each Host (which could be 100s-1000s) would be an especially
>good idea.

I believe we are in agreement both in terms of duration and the need to
have dynamic buffer management.  I will clarify that there will also be
sessions that are not host focused, e.g. the peer-to-peer direction of a
storage object to another device, e.g. multi-media streaming and these
sessions will be shorter lived - possibly on a per transaction basis where
a transaction is something of reasonably large in value (e.g. 100's MBs of
data movement).

Mike