On Mon, 17 Jan 2005, Janusz Zamecki wrote: > Hello! > > After days of googling I've gave up and decided to ask for help. > > The story is very simple: I have /dev/md6 raid1 array made of hdg and > hde disks. The resulting array is as fast as 1 disk only. Why would you expect it to be any faster? > Please check this out: > > hdparm -t /dev/hdg /dev/hde /dev/md6 > > /dev/hdg: > Timing buffered disk reads: 184 MB in 3.03 seconds = 60.76 MB/sec > > /dev/hde: > Timing buffered disk reads: 184 MB in 3.01 seconds = 61.08 MB/sec > > /dev/md6: > Timing buffered disk reads: 184 MB in 3.03 seconds = 60.74 MB/sec These are all good - nice fast disks too by the looks of it - best I've seen for a while is about 55MB/sec head bandwidth. > I've expected much better /dev/md6 performance (at least 100MB/s). I wouldn't - use RAID-0 if you want more performance. > It seems that md6 uses one drive only. This is the dstat output: As I understand it, it reads "chunksize" blocks from one drive, then switches to the other drive, then back again. Try a bigger read - eg: time dd if=/dev/md6 of=/dev/null bs=128K count=8192 but I don't think there are any real gains to be made with RAID-1 - your results more or less track everything I've seen and used with RAID-1 - ie. disk read speed is the same as reading from a single device, and never significantly faster. Good luck... Gordon - 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
