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 real 0m16.360s user 0m0.310s sys 0m11.780s 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 real 0m18.790s user 0m0.380s sys 0m14.750s So there's a penalty, sure, accounted for mostly in sys time, but it's only about 10%: small enough that I at least can ignore it in exchange for the administrative convenience of LVM. -- `... in the sense that dragons logically follow evolution so they would be able to wield metal.' --- Kenneth Eng's colourless green ideas sleep furiously - 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
