RE: single vs multiple channels for iSCSI commands

[John Matze <John.Matze@NSMG.VERITAS.com>]

As in Haifa, I again endorse the single connection approach.  Especially for
this version of the spec.  Multiple channels may increase performance but
this could also be handled with additional hardware or programming.  At this
point we don't need to supply any ammunition to shoot holes in the spec.  I
believe this issue alone will cause enough dialog to slow down and possible
suspend the spec from being approved. 

John

-----Original Message-----
From: Costa Sapuntzakis [mailto:csapuntz@cisco.com]
Sent: Tuesday, June 27, 2000 8:26 PM
To: scsi-tcp@external.cisco.com; ips@ece.cmu.edu
Subject: Re: single vs multiple channels for iSCSI commands



I would like to stake out a position against any approach that involves
using multiple simultaneous TCP connections per iSCSI session.

The design of iSCSI (and the hardware that implements it) becomes
significantly simpler when there is just 1 TCP connection/session.

Parallel paths in the network can still be exploited by setting up
multiple sessions with multiple TCP connections.

So far, I have heard of two applications that allegedly require strict
ordering: tape backup and remote asynchronous mirroring. New SCSI commands 
or even higher-layer techniques can be used to satisfy these applications.

For example, I have heard that some high-bandwidth tape applications blast
self-describing blocks of data to tape, making the order in which data
gets read/written to tape less relevant.

For the case of high bandiwdth remote asynchronous mirroring, a special
SCSI remote asynchrnous mirroring command set could be introduced.
I believe remote asynchronous mirroring principally consists of one
command: WRITE, so the command set would probably be small. 

Ditching multiple simultaneous connections/session would help convince us
of the correctness of iSCSI and allow us to move onto other important
issues and help the time to market. 

-Costa

App A. Possible remote asynch mirroring command sets

1) 1 CDB: ORDERED WRITE 

2) 3 CDBs:  WRITE UNCOMMITTED,  COMMIT, ABORT