Re: iSCSI: error recovery

[julian_satran@il.ibm.com]

Matt,

Correct - but why is the assumption that iffish. Why would an adapter want
to ack data it has still buffered?
How can it help and what  gets simpler?
Why would a tape controller doing a huge copy to a disk want to give up
such an evidently good feature?

Julo

Matt Wakeley <matt_wakeley@agilent.com> on 31/10/2000 00:46:05

Please respond to Matt Wakeley <matt_wakeley@agilent.com>

To:   IPS Reflector <ips@ece.cmu.edu>
cc:
Subject:  Re: iSCSI: error recovery




julian_satran@il.ibm.com wrote:

> Matt,
>
> I think I read your note and I still maintain that the target will fare
> better and the initiator does not have to do anything different.
>
> When failing over the initiator will reissue the command (including all
> scatter gather lists) to the new HBA. It is the target that will send
only
> the buffers he has and as long as the initiator is not scoreboarding it
> does not have to do anything different the second time than first.

You are making the *big* assuption that an iSCSI initiator will "confirm"
the
receipt of this "numbered" data after the data has been transfered to
initiator
host memory.  What if it's buffered on the card somewhere, and the card
dies
and the system fails over to a different card?  (or perhaps an I/O
subsystem
fails and the system "fails over" to a standby subsystem) How is the
initiator
going to be absolutely sure that the "partial" I/O on the first card plus
the
"partial" I/O on the second card equal a complete error free I/O?

Is this idea for something that rarely happens really worth the effort?  In
the
interests of simplicity, I propose that data not be numbered.


>
>
> It is the target that will benefit and it is the target's decision to
> number or not.
>
> Regards,
> Julo

-Matt