On Monday May 22, Dexter.Filmore@xxxxxx wrote: > I just dd'ed a 700MB iso to /dev/null, dd returned 33MB/s. > Isn't that a little slow? > System is a sil3114 4 port sata 1 controller with 4 samsung spinpoint 250GB, > 8MB cache in raid 5 on a Athlon XP 2000+/512MB. > Yes, read on raid5 isn't as fast as we might like at the moment. It looks like you are getting about 11MB/s of each disk which is probably quite a bit slower than they can manage (what is the single-drive read speed you get dding from /dev/sda or whatever). You could try playing with the readahead number (blockdev --setra/--getra). I'm beginning to think that the default setting is a little low. You could also try increasing the stripe-cache size by writing numbers to /sys/block/mdX/md/stripe_cache_size On my test system with a 4 drive raid5 over fast SCSI drives, I get 230MB/sec on drives that give 90MB/sec. If I increase the stripe_cache_size from 256 to 1024, I get 260MB/sec. I wonder if your SATA controller is causing you grief. Could you try dd if=/dev/SOMEDISK of=/dev/null bs=1024k count=1024 and then do the same again on all devices in parallel e.g. dd if=/dev/SOMEDISK of=/dev/null bs=1024k count=1024 & dd if=/dev/SOMEOTHERDISK of=/dev/null bs=1024k count=1024 & ... and see how the speeds compare. (I get about 55MB/sec on each of 5 drives, or 270MB/sec, which is probably hitting the SCSI buss limit which as a theoretical max of 320MB/sec I think) NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
