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    RE: iSCSI: No Framing

    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.
    > >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


Last updated: Tue Feb 05 23:17:59 2002
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