Raid allows for data to be sparsed over multiple disks and give security to your data as one (or more) disks can fail and data integrity will still remain.
mdadm --zero-superblock /dev/sd[b-e]
wipefs -a /dev/sd[b-e]
You can set level to get more performance or more redundancy
This command will create a raid level 10.
mdadm --create /dev/md0 --level=10 --raid-devices=4 /dev/sd[b-e]
Check raid types and benefits here: http://www.raid-calculator.com/
Save your newly created raid configuration for next reboots:
mdadm --detail --scan > /etc/mdadm/mdadm.conf
- cat /proc/mdstat: shows raid status and progress
mdadm software raid will trigger a complete check every sunday at 1am. Be aware of that as it will lower diks io speed a lot.