Luke Lonergan wrote: > > OK, how about some proof? > > In a synthetic test that writes 32GB of sequential 8k pages on a machine > with 16GB of RAM: > ========================= Write test results ============================== > time bash -c "dd if=/dev/zero of=/dbfast1/llonergan/bigfile bs=8k > count=2000000 && sync" & > time bash -c "dd if=/dev/zero of=/dbfast3/llonergan/bigfile bs=8k > count=2000000 && sync" & > > 2000000 records in > 2000000 records out > 2000000 records in > 2000000 records out > > real 1m0.046s > user 0m0.270s > sys 0m30.008s > > real 1m0.047s > user 0m0.287s > sys 0m30.675s > > So that's 32,000 MB written in 60.05 seconds, which is 533MB/s sustained > with two threads. > Well, since this is always fun (2G memory, 3Ware 7506, 4xPATA), writing: $ dd if=/dev/zero of=/data0/dump/bigfile bs=8k count=500000 500000+0 records in 500000+0 records out 4096000000 bytes transferred in 32.619208 secs (125570185 bytes/sec) > Now to read the same files in parallel: > ========================= Read test results ============================== > sync > time dd of=/dev/null if=/dbfast1/llonergan/bigfile bs=8k & > time dd of=/dev/null if=/dbfast3/llonergan/bigfile bs=8k & > > 2000000 records in > 2000000 records out > > real 0m39.849s > user 0m0.282s > sys 0m22.294s > 2000000 records in > 2000000 records out > > real 0m40.410s > user 0m0.251s > sys 0m22.515s > > And that's 32,000MB in 40.4 seconds, or 792MB/s sustained from disk (not > memory). > Reading: $ dd of=/dev/null if=/data0/dump/bigfile bs=8k count=500000 500000+0 records in 500000+0 records out 4096000000 bytes transferred in 24.067298 secs (170189442 bytes/sec) Ok - didn't quite get my quoted 175MB/s, (FWIW if bs=32k I get exactly 175MB/s). Hmmm - a bit humbled by Luke's machinery :-), however, mine is probably competitive on (MB/s)/$.... It would be interesting to see what Dan's system would do on a purely sequential workload - as 40-50MB of purely random IO is high. Cheers Mark
