Re: SMP/cc Cluster description

[Davide Libenzi]

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.

- Davide