RAID 1 consists of an exact copy (or mirror) of a set of data on two or more disks. A classic RAID 1 mirrored pair contains two disks. The array will continue to operate so long as at least one member drive is operational.

To create a  software RAID array can be used the mdadm utility

Install mdadm

Type the following command under RHEL / CentOS / Fedora Linux:

# yum install mdadm

Type the following command under Debian / Ubuntu Linux:

# apt-get update && apt-get install mdadm

Create the Array

# mdadm –create /dev/md0 –level=raid1 –raid-devices=2 /dev/sdb /dev/sdc 

You can check that your RAID was made successfully by executing the  command

# cat /proc/mdstat 

Create and Mount the Filesystem

Formatting a RAID drive using the MKFS command:

# mkfs.ext4 -F /dev/md0

Create a new folder for the RAID to mount to with the mkdir command.

# mkdir -p /mnt/raid1

Use the mount command and bind the RAID array to the new /mnt/raid1 folder.

# mount /dev/md0 /mnt/raid1

Add the new filesystem mount options to the /etc/fstab file for automatic mounting at boot:

# echo ‘/dev/md0 /mnt/raid1 ext4 defaults,nofail,discard 0 0’ | sudo tee -a /etc/fstab

Your RAID 1 array should now automatically be assembled and mounted each boot.