SUMMARY: Cluster vs. multiprocessing server...

        Hello,
thanks to the many responses on my query. Here was the question:

> Comparing two hypothetical systems:
>
>    1) A Sun (or Beowolf) cluster with 4 servers / 2 CPU's each, 4 GB each
> server  vs.
>    2) A server with 8 processors & 16GB of RAM.
>
> from a users point of view how do these two systems look different. Is
there
> any advantage of configuration 1 over 2 (or vice versa)? Assuming identical
> CPU speeds, etc.
>
> Can anyone point me to a good introduction of the benefits of Sun (or
> Beowulf) cluster technology?


Many people gave long and detailed answers. Thank you very much to everyone
who responded. The comments below are generalization! There are always
specific cases & instances where this or that does not apply. If I missed
something major feel free to email me. Advantages & disadvantages of the two
configurations:

  1)  Sun (or Beowolf) cluster with 4 servers / 2 CPU's each, 4 GB each

     Advantages:
        - Good failure protection since we have multiple systems.
        - Good for network intensive applications (web server)
        - Easy to scale to larger sizes.
        - Hardware tends to be cheaper than a single large server, though
          when Sun clustering software/maintenance cost is added overall
          cost may not be lower.
        - Intel/Linux Beowulf cluster can be low cost (hard to beat), but
          maintenance may be an issue.

     Disadvantages:
        - Requires substantial extra effort to configure software wise.
        - Sun Cluster software is very expensive.
        - Harder to find Beowulf cluster support.
        - Network I/O is slower than bus speeds. Performance penalty.
        - User still sees many different computers. Must split applications
          between cluster nodes. This is not true of a SMP cluster where a
          user would see one virtual system. I am not sure Sun offers SMP
          clusters.


   2) A server with 8 processors & 16GB of RAM.

     Advantages:
       - Simpler to configure and maintain.
       - Most "out-of-the-box" applications tend to run better on a single
          large system. Optimized cluster applications (commercial), such
          as a DB program, tend to be very expensive.
       - Fast I/O between processors & RAM since it all one system.
       - Less OS overhead & shared memory applications can benefit
          from single servers.

     Disadvantages:
       - Single system, less failover protection. Sun does have quite a bit
          redundancy build into their servers if properly configured.
       - Hardware is generally more expensive then a cluster.


Overall conclusion:

   - How and what software is used is critical in determining the best
choice.
   - If high-availability is the key, then go with cluster, otherwise a single
server will probably serve you better.
   - If expandability and low hardware cost is the key, then a cluster may be
a better solution.


Additional information:

    Additional cluster vendors:   Legato, Veritas
    Book: ``In Search of Clusters'' by Greg Pfister, 2nd edition was 1998.
    www.beowulf.org
    http://www.isc.tamu.edu/isc/main.html
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