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    SubjectRe: SMP/cc Cluster description
    also some applications (i.e. databases) are such that nobody has really
    been able to rewrite them into the shared nothing model (although oracle
    has attempted it, from what I hear it has problems)

    David Lang

    On Thu, 6 Dec 2001,
    Jeff V. Merkey wrote:

    > Date: Thu, 6 Dec 2001 12:34:48 -0700
    > From: Jeff V. Merkey <jmerkey@vger.timpanogas.org>
    > To: Davide Libenzi <davidel@xmailserver.org>
    > Cc: David S. Miller <davem@redhat.com>, lm@bitmover.com,
    > rusty@rustcorp.com.au, Martin J. Bligh <Martin.Bligh@us.ibm.com>,
    > Rik vav Riel <riel@conectiva.com.br>, lars.spam@nocrew.org,
    > Alan Cox <alan@lxorguk.ukuu.org.uk>, hps@intermeta.de,
    > lkml <linux-kernel@vger.kernel.org>, jmerkey@timpanogas.org
    > Subject: Re: SMP/cc Cluster description
    >
    > On Thu, Dec 06, 2001 at 11:11:27AM -0800, Davide Libenzi wrote:
    > > On Thu, 6 Dec 2001, Jeff V. Merkey wrote:
    > >
    > > > Guys,
    > > >
    > > > I am the maintaner of SCI, the ccNUMA technology standard. I know
    > > > alot about this stuff, and have been involved with SCI since
    > > > 1994. I work with it every day and the Dolphin guys on some huge
    > > > supercomputer accounts, like Los Alamos and Sandia Labs in NM.
    > > > I will tell you this from what I know.
    > > >
    > > > A shared everything approach is a programmers dream come true,
    > > > but you can forget getting reasonable fault tolerance with it. The
    > > > shared memory zealots want everyone to believe ccNUMA is better
    > > > than sex, but it does not scale when compared to Shared-Nothing
    > > > programming models. There's also a lot of tough issues for dealing
    > > > with failed nodes, and how you recover when peoples memory is
    > > > all over the place across a nuch of machines.
    > >
    > > If you can afford rewriting/rearchitecting your application it's pretty
    > > clear that the share-nothing model is the winner one.
    > > But if you can rewrite your application using a share-nothing model you
    > > don't need any fancy clustering architectures since beowulf like cluster
    > > would work for you and they'll give you a great scalability over the
    > > number of nodes.
    > > The problem arises when you've to choose between a new architecture
    > > ( share nothing ) using conventional clusters and a
    > > share-all/keep-all-your-application-as-is one.
    > > The share nothing is cheap and gives you a very nice scalability, these
    > > are the two mayor pros for this solution.
    > > On the other side you've a vary bad scalability and a very expensive
    > > solution.
    > > But you've to consider :
    > >
    > > 1) rewriting is risky
    > >
    > > 2) good developers to rewrite your stuff are expensive ( $100K up to $150K
    > > in my area )
    > >
    > > These are the reason that let me think that conventional SMP machines will
    > > have a future in addition to my believing that technology will help a lot
    > > to improve scalability.
    > >
    >
    > There's a way through the fog. Shared Nothing with explicit coherence.
    > You are correct, applications need to be rewritten to exploit it. It
    > is possible to run existing SMP apps process -> process across nodes
    > with ccNUMA, and this works, but you don't get the scaling as shared
    > nothing.
    >
    > Jeff
    >
    > Jeff
    >
    >
    > >
    > >
    > >
    > > - Davide
    > >
    > >
    > >
    > -
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