> procs. Within each process the accesses to their "cube" of data were > near to completely random.
"completely random" is a bit like von Neumann's "state of sin" ;) if they managed to make actually uniform random accesses, they'd have discovered a new PRNG, possibly the most conpute-intensive known! my guess is that apps that claim to be random/seeky often have pretty non-uniform patterns. they obviously have a working set, and the question is really how sharp the knee is in that curve. when the cache-miss penalty is large, such as ram vs casually-configured swap on a normal disks. what if there's a 1000x difference in how often used are the the hottest blcoks vs cool onnes? let's eyeball a typical memory latency at 50 ns, a mediocre disk at 10 ms, but the real news here is that completely mundane SSD latency is 130 us. 200,000x slower is why thrashing is painful - 2600x slower than ram is not something you can ignore, but it's not crazy. it's a curious coincidence that a farm of Gb servers could provide random 4k blocks at a latency similar to the SSD (say 150 us). of course, ScaleMP is, abstractly, based on this idea (over IB.) > IOPs, but is there anywhere a scaling study on them where individual > requests latencies are measured and CDF'd? That would be really http://markhahn.ca/ssd.png like this? those are random 4k reads, uniformly distributed. regards, mark. _______________________________________________ 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
