> 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. Changed from 384 to 1024, no improvement. > > You could also try increasing the stripe-cache size by writing numbers > to > /sys/block/mdX/md/stripe_cache_size Actually, there's no directory /sys/block/md0/md/ here. Can I find that in proc somewhere? And what are sane numbers for this setting? > 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 & > ... 4112 pts/0 R 0:00 dd if /dev/sda of /dev/null bs 1024k count 1024 4113 pts/0 R 0:00 dd if /dev/sdb of /dev/null bs 1024k count 1024 4114 pts/0 R 0:00 dd if /dev/sdc of /dev/null bs 1024k count 1024 4115 pts/0 R 0:00 dd if /dev/sdd of /dev/null bs 1024k count 1024 4116 pts/0 R+ 0:00 ps ax 1024+0 Datensätze ein 1024+0 Datensätze aus 1073741824 Bytes (1,1 GB) kopiert, 34,5576 Sekunden, 31,1 MB/s 1024+0 Datensätze ein 1024+0 Datensätze aus 1073741824 Bytes (1,1 GB) kopiert, 36,073 Sekunden, 29,8 MB/s 1024+0 Datensätze ein 1024+0 Datensätze aus 1073741824 Bytes (1,1 GB) kopiert, 40,5109 Sekunden, 26,5 MB/s 1024+0 Datensätze ein 1024+0 Datensätze aus 1073741824 Bytes (1,1 GB) kopiert, 40,5054 Sekunden, 26,5 MB/s (Partly german, but I think you get it) A single disks pumps out 65-70MB/s. Since they are on a PCI 32bit controller the combined speeds when reading from all four disks at once pretty much max the 133MB/s PCI limit. (I' surprised it comes so close. That controller works pretty well for 18 bucks.) Dex -- -----BEGIN GEEK CODE BLOCK----- Version: 3.12 GCS d--(+)@ s-:+ a- C+++(++++) UL+>++++ P+>++ L+++>++++ E-- W++ N o? K- w--(---) !O M+ V- PS++(+) PE(-) Y++ PGP t++(---)@ 5 X+(++) R+(++) tv--(+)@ b++(+++) DI+++ D G++ e* h>++ r%>* y? ------END GEEK CODE BLOCK------ http://www.stop1984.com http://www.againsttcpa.com - 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
