• with the instructions that follow we move a complete root system disk from bare partitions to a raid 1 software layer.
• all the work is done without putting the server off-line.
• only one reboot process is needed if the disks are already installed on the server.

• /dev/sda: is the original disk from where the system boot
• /dev/sdb: is the second disk

• we need to create the correct partitions we need:
  • 100 MB for the boot partition
  • 2Gbyte for the swap partition (there's no need to put the swap partitions on a raid system)
  • rest of the space disk for the root and others partitions

start fdisk

 fdisk /dev/sdb
 n
 p
 1
 [enter]
 +100M
 n
 p
 2
 [enter]
 +2048M
 n
 p
 3
 [enter]
 [enter]
 t
 2
 82
 t
 3
 fd
 w