1. Mark the disk as failed # mdadm --manage /dev/md0 --fail /dev/sdb1 To verify that the disk is failed, check /proc/mdstat: # cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid5] [raid4] [raid6] [raid10] md0 : active raid1 sda1[0] sdb1[2](F) 976773168 blocks [2/1] [U_] md1 : active raid1 sda2[0] sdb2[1] 976773168 blocks [2/2] [UU] Failed disk will be marked as “(F)”. 2. Remove the disk by mdadm # mdadm --manage /dev/md0 --remove /dev/sdb1 3. Replace the disk Replace the faulty disk with new one. 4. Copy the partition table to the new disk Copy the partition table to the new disk (Caution: This sfdisk command will replace the entire partition table on the target disk with that of the source disk – use an alternative command if you need to preserve other partition information): # sfdisk -d /dev/sda | sfdisk /dev/sdb 5. Create mirror Create the mirror of the disk: # mdadm --manage /dev/md0 --add ...