Robert Tompkins ([EMAIL PROTECTED]) said: > I am building a cluster and i was wondering what would be more important, > memory with lower latency (cas 2 compared to cas 3) or more memory( 512 > megs compared to 1 gig). Is memory latency a bottleneck in clustered > computering or is it usually memory size that is the bottleneck.
depends on your problem > Also would it be better to have 20 smp machines or 40 single > processor machines( both of which would be connected by > 100base-t). depends on your problem w/o knowing more about what you want to do with your beowulf, it's very hard to answer the (very good) questions you ask. It's why my employer is in business. *generally* you want fast memory. unless you are working with data structures so big that you might touch swap. *generally* you will never see 100% utilization of the second cpu in an smp node. 60% is more normal, but i've seen it get as high as 95%. two cpus have to contend for the memory bus, and on x86, the memory bandwidth is already pitifully small. 2 cpus have to contend for the one network pipe going into the node. basically every shared resource represents a *potential* bottleneck ( only your applcation can say if it really is a limit). sometimes jobs running on the 2 cpus can share memory ( some incarnations of mpich support this, i belive, if you configure with the right flags ), but not often. If you can, get 4 nodes: permute smp and up with slow ram and big ram. it won't reflect the communications overhead, but you can start to measure the effect hardware has on your problem: you might find the slow ram to have a negligible impact on run time for example. good luck ==rob -- Rob Latham: linux A-Team Bethlehem, PA USA EAE8 DE90 85BB 526F 3181 1FCF 51C4 B6CB 08CC 0897
