RE: iSCSI: No Framing

["Douglas Otis" <dotis@sanlight.net>]

Rob,

I agree with your conclusions.  10 TB/day would represent an average of
about 1 Gb/sec.  This would be possible within a MAN environment.  Indeed,
within that environment and through the use of specialized memory handling,
the need for any framing technique quickly vanishes.

Doug

> >Rob,
> >
> >Although it will be true large amounts of bandwidth will be exchanged
> >between the typical SAN, such systems also use cache due to mechanical
> >limitations with respect to rotation and linear access.  If it were
> >just storage to storage, Fibre-Channel or FC encapsulation would be
> >preferable. At least with that scheme, there are direct placement
> >interfaces available.
>
> Without bogging down the list in a debate about storage subsystems, I must
> say that there are examples to the contrary w.r.t. the usage of subsystem
> cache.
>
> iSCSI is, of course, more than just storage-to-storage.  But we should not
> limit iSCSI to just host-to-storage.  Remember, storage subsystems can
> (and are, in some cases) both initiator and target at the same time.
>
> The original thread began with a question (paraphrased) about '...what
> applications could consume a 10G pipe for long periods of time'.
> I answered that question - disk-disk backup and subsystem replication.
>
> FC is not sufficient.  Storage-to-storage needs all the advantages as well
> as that which iSCSI has to offer the host-storage model.
>
> > Direct placement is needed with low latency high bandwidth to reduce
> > overhead loss during a subsequent memory copy.
>
> This assumes a subsequent memory copy.
>
> >SCTP offers a means of implementing direct placement without kludging
> >a portion of the application beneath the transport.  In addition,
> >this direct placement scheme can be done in an general fashion to
> >support thousands of higher level protocols. As with most SAN,
> >network related failures are not well tolerated, so the added
> >robustness of SCTP becomes highly beneficial.
>
> Having read this list since its creation, I choose to not
> participate in the SCTP/TCP religious war.
>
> >In establishing a large remote mirror, the highest bandwidth means of
> >initialization would be physical transport of the image.  Once
> >initialized, only differential information is exchanged largely
> >limited by the bandwidth and error rate of the interconnect.
>
> Well put.  Consider 3-10 TB of differential per day as a start.  Consider
> images of 100s to 1,000s of TB, spread across 100s to 1,000s of 15KRPM (or
> more, stay tuned) spindles.  Now, we're talking.
>
> Rob
>
> Rob Peglar
> Corporate Architect
> XIOtech Corporation, a Seagate Company
> (314) 308-6983