On 2/10/11 11:52 AM, Stuart Barkley wrote: > 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? >
Our weather/hurricane codes are memory bound, so yes we worry about it. We aren't installing so much memory that we are paying a price premium to ensure only one channel is filled, so it isn't a big deal. Have we tested it? No. But we haven't had to. Craig > 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 _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
