[Beowulf] Advice on 4 CPU node configurations

[Stuart Barkley]

On Wed, 9 Feb 2011 at 09:38 -0000, Prentice Bisbal wrote:

> About 6 months ago, I purchased a couple of Dell PowerEdge R815s
> with 128 GB of RAM and 32 cores. We looked at similar RAM
> configurations a couple of years ago. and the cost premium for that
> much RAM was prohibitive (the price for additional RAM seemed to go
> up exponentially with the amount of RAM) so we stayed at 32 GB.
> This time around, the premium for the additional RAM seemed
> marginal. Not sure how large you can go and keep that "marginal"
> relationship, but it's much larger than it was a couple of years
> ago.

How much does the RAM speed matter to people?

We have a lot of 2 CPU (8 core) systems and have been considering
memory upgrades (or just purchasing new systems with more memory since
we are still growing).

Currently we are running 1 4GB DIMM per channel at 1333 MHz.  If we
add a second 4GB DIMM per channel then the memory will run at 1066 MHz
(and to 800 MHz with 3 DIMMs per channel).  Alternatively, we could
replace the 4GB modules with 8GB ones (keeping the old ones for spares
or to side-grade some other machines to 48GB/1066 MHz).

Have people been worrying about the lower memory bus rate with
multiple DIMMs on each channel?  Do "ordinary" applications notice the
difference?

I know it depends upon the application and I have no idea if this will
matter to our applications.  Mostly, I just happy things are running
at all rather than fighting every ounce of performance.

Stuart Barkley
-- 
I've never been lost; I was once bewildered for three days, but never lost!
                                        --  Daniel Boone