RAID5 - mirror c partition

[ozydave]

HI

I have a Proliant ML150G2 with 4 160Gb drives in a hardware raid 5. (it is our main domain controller – we do have a backup domain controller)
The array have been split into 3 so the c (system) partition is part of the raid 5. Not ideal I know, it was already setup when I got here.
I want to get a mirror of the system partition (c Drive).
What is the best way? Can I just add another dive and then use windows disk manager to mirror c:
Will it work if I attach an external hard drive and then use windows disk manager to mirror c:

Fairly new to RAID so not sure what the best method is – I don’t want to start from scratch

Many Thnaks

[Víctor Cespón]

This is a disk cloning question, not a RAID question. You have 3 logical units or a logical units with 3 partitions?
Anyway, there are programas like Acronis TrueImage that can perform a copy of a partition to another partition or a file. This works with USB hard disks too.