First, add disks before making RAID(Link).
And.. This is simple description of RAID(Link).
I tested these on CentOS 7. The order is "Creating RAID device" → "Format" → "Mount".
❑ RAID related mdadm commands
❍ mdadm --detail --scan : RAID status.
❍ mdadm --detail /dev/md9 : The md9 RAID device Details.
❍ mdadm --run /dev/md9 : Start the md9 RAID device.
❍ mdadm --stop : Stop the md9 RAID device.
❍ mdadm /dev/md1 --add /dev/sdc1 : If one of the devices that make up the RAID has a problem, how to add and recover the device.
❑ How to make a Linear RAID
❍ Creating RAID device : mdadm --create /dev/md9 --level=linear --raid-devices=2 /dev/sdb1 /dev/sdc1
❍ Format(ext4) : mkfs.ext4 /dev/md9
❍ mount(Manual/Temporary) : mount /dev/md09 /myRAID1
❍ mount(Auto/Permanent) : /dev/md9 /myRAID1 ext4 defaults 0 0(Add this in "/etc/fstab" and reboot the system)
❑ How to make a RAID 0
❍ Creating RAID device : mdadm --create /dev/md9 --level=0 --raid-devices=2 /dev/sdd1 /dev/sde1
❍ Format(ext4) : mkfs.ext4 /dev/md9
❑ How to make a RAID 1+0
❍ Creating RAID 1 device : mdadm --create /dev/md2 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1
❍ Creating RAID 1 device : mdadm --create /dev/md3 --level=1 --raid-devices=2 /dev/sdc1 /dev/sdd1
❍ Creating RAID 0 device : mdadm --create /dev/md4 --level=0 --raid-devices=2 /dev/md2 /dev/md3