RE: single vs multiple channels for iSCSI commands

["Hughes, James P. (MRDC)" <HugheJP@nsc-bridge.network.com>]

I agree. One TCP connection with command and data mixed. Keep it simple. The
need to go out of order is so small that we should not let this "wag the
dog".

In addition, we need to have centralized control of devices. That is, a tape
drive needs to be given out by a controlling authority, and this needs to be
stronger than just cookies. IPSEC and SSL need another layer to determine
who owns a peripheral.

Jim


-----Original Message-----
From:	Costa Sapuntzakis [mailto:csapuntz@cisco.com]
Sent:	Tuesday, June 27, 2000 10:26 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