mdadm --manage /dev/md125 -a /dev/sdb4
mdadm: add new device failed for /dev/sdb4 as 3: Invalid argument
Dec 19 01:23:48 storageboxtest kernel: [ 2328.854491] md: sdb4 does not have a valid v1.2 superblock, not importing!
Dec 19 01:23:48 storageboxtest kernel: [ 2328.854499] md: md_import_device returned -22
#zero the superblock and try again!
mdadm --zero-superblock /dev/sdb4
mdadm --ma........