Re: Connection Consensus Progress

[julian_satran@il.ibm.com]

David,

I understand and share your concerns about how good we understand the
requirements for recovery and balancing.

But as I stated repeatedly we can't wait for somebody else to solve our
problem and the
field requirement is there as witnessed by the products that attempt to
solve it in a
proprietary fashion (and BTW a TCP connection failure could also be
repaired simply by
TCP but TCP does not do it).

However if they are there the both sets have to be solved at SCSI level -
since several links
if not handled properly increase the failure probability.

However your last point about multiple HBAs is lost on me.
We attempted to make iSCSI work with several HBAs and went to some length
to keep
the requirements to the HBA hardware as if the HBAs act independently
(counters can be
shared). Is there something we missed?

Julo

David Robinson <David.Robinson@EBay.Sun.COM> on 25/08/2000 23:32:23

Please respond to David Robinson <David.Robinson@EBay.Sun.COM>

To:   ips@ece.cmu.edu
cc:    (bcc: Julian Satran/Haifa/IBM)
Subject:  Re: Connection Consensus Progress




> I agree with you up to a point.  I know of customers that always need
> multiple physical paths to the Storage Controller.  Regardless of how
fast
> the link is, they need a faster link, and these hosts need to be able to
> spread the load across several different HBAs.  (Some are on one PCI bus,
> and some on another, etc.)  When this happens, as it does today, with
Fibre
> Channel, we are required, as are a number of other vendors, to come up
with
> a multi HBA balancer.  We call our Fibre Channel version "DPO" (Dynamic
> Path Optimizer), EMC has another version (I do not know what they call
> theirs).  This Code sits as a "Wedge" Driver above the FC Device Drivers
> and balances the work across the different FC HBAs.  I think this same
> thing will be required in the iSCSI situation.  Note:I think, the FC
> versions only work with IBM or EMC's etc. Controllers.  (SUN probably has
a
> similar one also.)

I understand this scenerio, it is often used as a high availability
feature.
The key question is if this should be handled above at the SCSI layer
as it is most often done now, or in the iSCSI transport. While I like
the goal to unify this into one architecture, I have serious doubts that
we have the understanding of the requirements and needs necessary
to get it right.  Thus we will ultimately end up in the same situation
we are in today with a SCSI layer solution.  In addition, if the promise
of a hardware iSCSI NIC/HBA is acheived, allowing multiple paths using
different NIC/HBAs will still require "wedge" software.

     -David