echo frozen >/sys/block/md1/md/sync_action

In my experience, this will potentially set your RAID volume to "Degraded" state, without an option to restart the rebuilding in the Web GUI.

Start rebuilding the QNAP RAID storage Volume can be done by command line like so:

echo "idle" > /sys/block/md1/md/sync_action

if that doesn't work, then you can try:

echo "recover" > /sys/block/md1/md/sync_action

** md1 being the array you found with "cat/proc/mdstat" 😊 

The resynchronization of your RAID group is there for reason!
(bad disk, bad block, raid out of sync etc).

Having said that, If your array is md2 then

echo "idle" > /sys/block/md2/md/sync_action

You can determine which is your array by using:

cat /proc/mdstat

In the example below you'll see that md2 is my RAID-6 array ...

 # cat /proc/mdstat                                                      
Personalities :         
md2 : active raid6 sdg3 sde3 sdf3 sdd3 sdc3 sdh3 sdj3 sdi3
      23382380544 blocks super 1.0 level 6, 512k chunk, algorithm 2  
      bitmap: 12/30 pages , 65536KB chunk

md1 : active raid0 sda3 sdb3
      956863488 blocks super 1.0 512k chunks
      
md322 : active raid1 sde5(S) sdf5(S) sdd5(S) sdc5(S) sdh5(S) sdj5(S) sdi5 sdg5
      7235136 blocks super 1.0  
      bitmap: 0/1 pages , 65536KB chunk

....

unused devices: