On Mon, 11 Jun 2007, Nix wrote: > On 11 Jun 2007, Justin Piszcz told this: > > You can do a read test. > > > > 10gb read test: > > > > dd if=/dev/md0 bs=1M count=10240 of=/dev/null > > > > What is the result? > > > > I've read that LVM can incur a 30-50% slowdown. > > FWIW I see a much smaller penalty than that. > > loki:~# lvs -o +devices > LV VG Attr LSize Origin Snap% Move Log Copy% Devices > [...] > usr raid -wi-ao 6.00G /dev/md1(50) > > loki:~# time dd if=/dev/md1 bs=1000 count=502400 of=/dev/null > 502400+0 records in > 502400+0 records out > 502400000 bytes (502 MB) copied, 16.2995 s, 30.8 MB/s > > loki:~# time dd if=/dev/raid/usr bs=1000 count=502400 of=/dev/null > 502400+0 records in > 502400+0 records out > 502400000 bytes (502 MB) copied, 18.6172 s, 27.0 MB/s And what is it like with 'iflag=direct' which I really feel you have to use, otherwise you get caching. -- Jon Nelson <jnelson-linux-raid@xxxxxxxxxxx> - 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
