ubuntu 17.04 configures RAID 5 after OS installation

Using 3 or 4 drives in an array to add redundancy and increase performance.

Drives can be different sizes, allocate same sizes partitions.

If WD drives, never use GREEN.  First choice RED, or at least BLACK BLUE).

ref: How To Create a Software RAID 5 in Linux Mint / Ubuntu | PCsteps.com