RE: iSCSI Requirements Draft - Informal WG Last Call

[Black_David@emc.com]

Santosh,

Objection noted - could you attempt to write
alternative text that would respect the original
motivation to avoid reordering of commands in
most situations without causing the problems
that concern you in error cases?  Fibre Channel
may be a useful analogy, as FC delivers in order
as long as there isn't a frame drop or CRC
failure (both of which are very rare events).

Thanks,
--David

> -----Original Message-----
> From:	Santosh Rao [SMTP:santoshr@cup.hp.com]
> Sent:	Thursday, April 12, 2001 9:34 PM
> To:	ips@ece.cmu.edu
> Cc:	Black_David@emc.com
> Subject:	Re: iSCSI Requirements Draft - Informal WG Last Call
> 
> David & All,
> 
> I object to the following requirement :
> 
> " MUST support ordered delivery of SCSI commands from the initiator to
> the 
>   target, to support SCSI Task Queuing. "
> 
> Ordered delivery is not a requirement for disk based applications and
> non tagged queueing tape applications, which form the majority of
> today's data traffic. 
> 
> To impose strict ordering (even in the presence of errors ?) as a MUST
> is penalizing the majority of today's data traffic that does not expect
> ordering from the SCSI subsystem.
> 
> I am particularly concerned about the effect of the above requirement in
> the presence of errors. Does iSCSI expect strict ordering to be
> maintained even when individual I/O errors like ULP timeout occur ? 
> 
> On a ULP timeout (caused by, say, a hole in CmdSN), the initiator may
> choose not to retry the command, but instead, error it back to the ULP.
> In such a case, it can plug the hole in CmdSN with a NOP-OUT.
> 
> The above requirement is not feasible to be met under such circumstances
> and others similar to this. Mandating strict ordering on ULP timeouts
> implies a session level error recovery on any individual I/O being
> failed back from iSCSI to SCSI ULP. This is a very heavy hammer to use
> as error recovery and should not be imposed.
> 
> The above requirement must be changed to :
> " SHOULD support ordered delivery of SCSI commands from the initiator to
> the 
>   target, to support SCSI Task Queuing. "
> 
> - Santosh
> 
> 
> 
> Black_David@emc.com wrote:
> > 
> > It is intended to submit draft-ietf-ips-iscsi-reqmts-02.txt
> > as an Informational RFC. There is no formal requirement for
> > a WG Last Call, but if you have any further substantive comments
> > on the document please raise them on this list within the next
> > two weeks, i.e. by April 27th at the latest.
> > 
> > If you have typographical/editorial comments please send them
> > direct to the document's author, Marjorie Krueger
> > <marjorie_krueger@hp.com>.
> > 
> > Thanks,
> > --David and Elizabeth, IPS WG co-chairs << File: Card for Santosh Rao >>
>