On Tuesday August 22, brad@xxxxxxxxxxx wrote: > G'day all, > > I have a box with 15 SATA drives in it, they are all on the PCI bus and it's a relatively slow machine. > > I can extract about 100MB/s combined read speed from these drives with dd. > > When reading /dev/md0 with dd I get about 80MB/s, but when I ask it to check the array on a > completely idle system with echo check > /sys/block/md/md0/sync_action I get a combined read speed > across all drives of 31.9MB/s > > I'm not that fussed I guess, given the system does have extended idle periods, it would be nice to > have a sync or check complete as quickly as the hardware allows. Experience has shown that a rebuild > of a single disk failure takes 10-12 hours but the check seems to take forever > > brad@storage1:~$ cat /proc/mdstat > Personalities : [raid6] > md0 : active raid6 sda[0] sdo[14] sdn[13] sdm[12] sdl[11] sdk[10] sdj[9] sdi[8] sdh[7] sdg[6] sdf[5] > sde[4] sdd[3] sdc[2] sdb[1] > 3186525056 blocks level 6, 128k chunk, algorithm 2 [15/15] [UUUUUUUUUUUUUUU] > [>....................] resync = 0.1% (458496/245117312) finish=1881.9min speed=2164K/sec Hmm.... nothing obvious. Have you tried increasing /proc/sys/dev/raid/speed_limit_min:1000 just in case that makes a difference (it shouldn't but you seem to be down close to that speed). What speed in the raid6 algorithm used - as reported at boot time? Again, I doubt that is the problem - if should be about 1000 times speed you are seeing. What if you try increasing /sys/block/md0/md/stripe_cache_size ? That's all I can think of for now. NeilBrown - 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
