This assumes that sdb has failed, the active drive is sda   Mark the drive as Failed mdadm /dev/md0 --fail /dev/sdb3 mdadm /dev/md1 --fail /dev/sdb1 Remove the drive from RAID array mdadm /dev/md0 --remove /dev/sdb3 mdadm /dev/md1 --remove /dev/sdb1 Create a new partitions for the new drive (sdb ) Method 1: Copy partition table from the good drive sfdisk -d /dev/sda | sfdisk /dev/sdb Method 2: Restore partition table from a backup file sfdisk /dev/sdb < /backup/sdb.partition Method 3: Create partitions manually Show status of the good drive (sda) for reference fdisk -l /dev/sda Create a new partitions for the new drive (sdb ) Start fdisk /dev/sdb New Partition n   Primary p   Partition Number 1   Start Cylinder 1   End Cylinder 13 New Partition n   Primary p   Partition Number 2   Start Cylinder 14   End Cylinder 144 New Partition n   Primary p   Partition Number 3   Start Cylinder 145   End Cylinder 1044 Partition Type t   Partition Number 1   RAID fd Partition Type t   Partition Number 2   swap 82 Partition Type t   Partition Number 3   RAID fd Toggle boot flag a   Partition Number 1 Write and Exit w Review the partition table of both drives fdisk -l Add RAID members mdadm /dev/md0 --add /dev/sdb3 mdadm /dev/md1 --add /dev/sdb1 Check Rebuild Status cat /proc/mdstat After rebuild, create stage 1 grub on sdb grub find /grub/stage1 device (hd0) /dev/sdb root (hd0,0) setup (hd0) quit