Re: Data in SCSI Response or SCSI Data

[julian_satran@il.ibm.com]

Is there anything preventing your hypothetical hardware implementor
to send always good status within the last block of data?

Does the hardware implementor make more decisions when finding status
allone in a response block or within the header of the last block?

Software based initiators will be, IMHO, a very important part of the
market -
to have them go through two calls is not wise.

On the other hand I am not religious about it.

However - sending "good status"
with the last piece of data has been part of the the I/O scene for a long
time
and I did attempt to keep the status quo.

Julo


Stephen Bailey <steph@cs.uchicago.edu> on 25/08/2000 19:14:48

Please respond to Stephen Bailey <steph@cs.uchicago.edu>

To:   ips@ece.cmu.edu
cc:    (bcc: Julian Satran/Haifa/IBM)
Subject:  Re: Data in SCSI Response or SCSI Data




> Again I have to agree.  Not everyone writing this protocol is developing
a
> hardware device.  Every time I (or any hardware vendor) sends one less IP
> packet down the wire is one less chance of it getting lost.

I do not think concessions should be made to software implementations
at the expense of hardware implementations.  Our experience is nobody
cares about a software network storage implementation if there are not
also hardware implementations.  The value proposition completely dries
up.  With available hardware implementations software implementations
become interesting.

I agree with Y.P. Cheng that implementing hardware for three ways to
find status IS a going to be a substantial irritation.  More
importantly, the outbound path of a hardware implementation (which
will include most targets) is very likely to chose to implement the
single easiest way for it, and use it in all cases.  In other words,
if data in one packet with RDMA information and status in a second
packet without is the natural way (seems like it), that's what you're
going to get coming back to the initiator.  Your software `fast path'
will never get exercised.

Even host `software' implementations are going to be able to support
various levels of hardware acceleration.  In the case of using a
hardware accelerated adapter, the host software will not see the data
packet, only the status.

Steph