md126 : active raid1 sdk2[1](F) sdb2[2]
9767448 blocks super 1.2 [2/1] [U_]
bitmap: 0/1 pages [0KB], 65536KB chunk
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# mdadm -a /dev/md126 /dev/sda2
mdadm: /dev/md126 has failed so using --add cannot work and might destroy
mdadm: data on /dev/sda2. You should stop the array and re-assemble it.