Re: ImmediateData Text Parameter Negotiation

[Santosh Rao <santoshr@cup.hp.com>]

The default settings should be conservative. Anyone offering advanced features
must be preapred to do extra work to offer the same and this involves having to
explicitly negotiate those keys to set it to aggressive values.

In keeping with other scsi models such as scsi mode page settings, defaults
must always be set to conservative values.

- Santosh


"Wheat, Stephen R" wrote:

> As both an iSCSI Target and RAID building blocks supplier, I agree with John
> and Sandeep that ImmediateData=Yes as default.  In particular, for the very
> reasons attributed to John below.
>
> Stephen
>
> -----Original Message-----
> From: Dave Sheehy [mailto:dbs@acropora.rose.agilent.com]
> Sent: Wednesday, September 19, 2001 4:12 PM
> To: ips@ece.cmu.edu
> Subject: Re: ImmediateData Text Parameter Negotiation
>
> >
> > I'd prefer "yes" as the default.
> >
> > Targets with memory constraints should limit the
> > maxCmdSN they advertise (allow only one cmd in the
> > worst case.. )
> >
> > What are the other reasons why "no" would be preferred ?
>
> Historical I suppose. Fibre Channel initially didn't support immediate or
> unsolicited data. Unsolicited data cannot be directly placed so it requires
> extra work and buffering on the part of the target which isn't readily
> accelerated in HW and Fibre Channel's emphasis was on enabling HW
> acceleration.
>
> Recently (relatively anyway), FCP-2 added immediate data commands back into
> Fibre Channel and some Fibre Channel folks mentioned on this list that it
> was a good thing. Yet, to date, I have seen no customer interest in that
> functionality so it makes me wonder what the fuss is about.
>
> John's argument has been that we need immediate/unsolicited data in order to
> fill long fat pipes. He also has said the extra work required on the target
> side is worth it. I want to test those notions with the other systems and
> peripheral (e.g. storage array) vendors.
>
> Dave Sheehy
>
> >
> > -Sandeep
> >
> > > > Additionally, I feel that the default value for ImmediateData should
> be
> > > > "no".
> > >
> > > This comes down to what do we think the most common default behavior is
> > > going to be. So far IIRC, the only person who has explicitly stated that
> > > immediate data support will be the common default behavior has been John
> > > Hufferd. I'd like to hear the opinions of the rest of the list.
> > >
> > > Dave Sheehy
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