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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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