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After investigating a load spike on my CentOS 7 server, I ran atop and noticed something odd. It is reporting MDD for my logical volume (md127) maxed out at 100% all the time.

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The other disk tests I ran seemed fine. It is a RAID1 config with two 500G SD drives. Any suggestions why this might be? It looks like it has been this way for a while.

[root@ds2 ~]# cat /proc/mdstat
Personalities : [raid1]
md126 : active raid1 sdb3[2] sda3[0]
      1049536 blocks super 1.0 [2/2] [UU]
      bitmap: 0/1 pages [0KB], 65536KB chunk

md127 : active raid1 sda2[0] sdb2[2]
      478291968 blocks super 1.2 [2/2] [UU]
      bitmap: 3/4 pages [12KB], 65536KB chunk

unused devices: <none>
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Mine is doing the same with RAID 1 config. It however does not seem to generate any load on the system. I ran 'sar' and %iowait is also below 0.5% at all times.

I can assume this is normal behaviour for RAID 1?

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