RHEL6 SoftRaid Replacing a Failed Hard Drive

1. Manually fail a hard drive

#mdadm /dev/md0 -f /dev/sdb

2. Remove the damaged hard drive:

#mdadm /dev/md0 -r /dev/sdb

3. Add a new hard disk to an existing array

mdadm /dev/md1 -a /dev/sdd

Notice:

#The newly added hard disk needs to be the same size as the original hard disk

#If the original array lacks working disks (for example, raid1 has only one working disk, and raid5 has only two working disks), then the newly added disk becomes the working disk directly. If the original array works normally, the newly added disk is hot backup disk.

refer to

http://www.toxingwang.com/linux-unix/linux-basic/1048.html