Replacing a faulty disk in a software RAID array on Linux
Setting a disk faulty/failed:
# mdadm --fail /dev/md0 /dev/hdb1
NOTE
DO NOT run this on a raid0 device or you will use your data
Removing a faulty disk from an array:
# mdadm --remove /dev/md0 /dev/hdb1
Clearing any previous raid information on a previously used disk
# mdadm --zero-superblock /dev/hdb1
Adding a disk to an array
# mdadm --add /dev/md0 /dev/hdb1