If you need to stop a resync of an MD array, the easiest way to do it is:
echo “idle” > /sys/block/md0/md/sync_action && mdadm –manage /dev/md0 –fail /dev/sda1
Revise the above based on the number of your array and the device that you want to mark as failed. Without the &&, the resync will resume right away. The above will stop the sync and mark the other disk as failed, which can be fixed later.