Is a mdadm check on your trusty software RAID array happening at the worst time and slowing down your server or NAS?

cat /proc/mdstat
Personalities : [raid1] [raid10]
md127 : active raid10 sdb4[0] sda4[1]
      897500672 blocks super 1.2 2 near-copies [2/2] [UU]
      [==========>..........]  check = 50.4% (452485504/897500672) finish=15500.3min speed=478K/sec
      bitmap: 5/7 pages [20KB], 65536KB chunk

Solution

Just tell it to idle"

echo idle >  /sys/devices/virtual/block/md127/md/sync_action
 

After that check again and you'll see it has stopped.

cat /proc/mdstat
Personalities : [raid1] [raid10]
md127 : active raid10 sdb4[0] sda4[1]
      897500672 blocks super 1.2 2 near-copies [2/2] [UU]
      bitmap: 5/7 pages [20KB], 65536KB chunk

 

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