This is a quick guide to setting up a Linux software RAID mirror (aka RAID 1).
There are a couple of toolsets for managing raid on Linux, raidtools and mdadm. This guide will use mdadm because imho it has better commands and features for monitoring.
Right, first you’ll need a couple of disk partitions of about the same size. These should be on separate disks or you’ll be defeating the point of raid mirroring