I have a server with Debian 6 and software RAID1. There is a problem: every few seconds the jbd2/md2-8 process loads all the HDD IO. It was detected by iotop. And for the md2_raid1 process 99% of IO displays.

The flush-9:2 process every few seconds loads 99% of CPU in top.

What can I do to optimize this system? Can transition to hardware RAID help in this situation?

This is cat /proc/mdstat

Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md3 : active raid1 sda4[0] sdb4[1]
      1822442815 blocks super 1.2 [2/2] [UU]

md2 : active raid1 sda3[0] sdb3[1]
      1073740664 blocks super 1.2 [2/2] [UU]

md1 : active raid1 sda2[0] sdb2[1]
      524276 blocks super 1.2 [2/2] [UU]

md0 : active raid1 sda1[0] sdb1[1]
      33553336 blocks super 1.2 [2/2] [UU]

unused devices: <none>
  • 1
    Yes, transitioning to hardware RAID would help the situation. May 11, 2012 at 7:58
  • have the same problem, my disks seem to be ok, I checked them with smartctl. It is really strange because the box becomes unresponsive
    – Janning
    Jun 12, 2012 at 14:55

2 Answers 2


next time this happens, run the following command "cat /proc/mdstat" then paste the output here

  • I have pasted it in main text
    – Andre-487
    May 13, 2012 at 17:07
  • Hello, sorry that I had never responded, was looking around just now, and it seems that something called noflushd can cause issues like what you are describing. Check out this article to see what I am talking about linuxquestions.org/questions/debian-26/… Feb 2, 2013 at 20:18

Your software raid is taking all the CPU cycles in order to run the RAID. Getting a hardware RAID can help. Keep in mind that if you want to take full advantage of a RAID controller you will need to ensure it has a BBU (battery back up) in order to enable the cache and write-back mode.

Depending on what is important to you, you could turn on RAID 0 (striping) and get even better performance out of your system, but even a regular RAID hardware controller will help.

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