On Feb 19, 2008 1:41 PM, Oliver Martin <oliver.martin@xxxxxxxxxxxxxxxxxxxx> wrote: > Janek Kozicki schrieb: > > hold on. This might be related to raid chunk positioning with respect > > to LVM chunk positioning. If they interfere there indeed may be some > > performance drop. Best to make sure that those chunks are aligned together. > > Interesting. I'm seeing a 20% performance drop too, with default RAID > and LVM chunk sizes of 64K and 4M, respectively. Since 64K divides 4M > evenly, I'd think there shouldn't be such a big performance penalty. > It's not like I care that much, I only have 100 Mbps ethernet anyway. > I'm just wondering... > > $ hdparm -t /dev/md0 > > /dev/md0: > Timing buffered disk reads: 148 MB in 3.01 seconds = 49.13 MB/sec > > $ hdparm -t /dev/dm-0 > > /dev/dm-0: > Timing buffered disk reads: 116 MB in 3.04 seconds = 38.20 MB/sec I'm getting better performance on a LV than on the underlying MD: # hdparm -t /dev/md0 /dev/md0: Timing buffered disk reads: 408 MB in 3.01 seconds = 135.63 MB/sec # hdparm -t /dev/raid/multimedia /dev/raid/multimedia: Timing buffered disk reads: 434 MB in 3.01 seconds = 144.04 MB/sec # md0 is a 3-disk raid5, 64k chunk, alg. 2, using a bitmap comprised of 7200rpm sata drives from several manufacturers. -- Jon - 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
