I'm trying to rsync a RAID 1 on a system with absolutely nothing running ( i've moved all services to another server ). So it's just me via ssh. For some reason, it's very slow:

cat /proc/mdstat

Personalities : [raid1]
md1 : active raid1 sdc1[1] sda1[0]
      104320 blocks [2/2] [UU]

md2 : active raid1 sdd1[1]
      1953511936 blocks [2/1] [_U]
      bitmap: 10/233 pages [40KB], 4096KB chunk

md0 : active raid1 sdc3[1] sda3[2]
      240814272 blocks [2/1] [_U]
      [>....................]  recovery =  1.0% (2488576/240814272) finish=8243.9min speed=479K/sec
      bitmap: 94/230 pages [376KB], 512KB chunk

unused devices: 

I already tried:

  • Setting /proc/sys/dev/raid/speed_limit_min to a very high value
  • Setting --bitmap=internal

None of these worked.

I also run smartctl on all HDs, no errors were detected. They seem fine. Hdparm also reports an average speed of 4000MB/s for reads. Which seems acceptable.

Any ideas of what might be happening?

I'm running centos 5.5 and my kernel is 2.6.18-274.7.1.el5.028stab095.1.

  • How big are the disks? What make/model are they? Commented Dec 31, 2011 at 17:45
  • /dev/sda and /dev/sdc are Hitachi Deskstar T7K250 series ( 250GB ).
    – Fernando
    Commented Dec 31, 2011 at 18:07
  • I think there were issues with mdadm and CentOS 5.5 (fixed in 5.6) - why did you not upgrade? Current Version is 5.7.
    – Nils
    Commented Dec 31, 2011 at 22:12
  • @Fernando what was your solution? Commented Jan 2, 2017 at 17:09

2 Answers 2


Probably a silly question, but have you verified that the speed_limit_max is also sufficiently high? 4000MB/s would be blindingly fast, that must be the cached speed not the actual disk speed.

  • Agreed. My guess is that the maximum is set to 500kbps, which you seem to be hovering near.
    – Scrivener
    Commented Jan 11, 2012 at 4:36

md1 is on the same physical device with md0, which is rebuilding. Are you sure there is also no activity on md0 ? Disk access on md1 can be slowing down the resync operation on md0

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