On Thu 22 Apr 1999, Erik E. Fair wrote:
> I've read the raid(4) and raidctl(8) man pages, and neither really answers
> this simple question:
> 
> I have two disks, I want to be protected against one of them failing, so
> some sort of mirror or redundancy is required. It looks like RAID level 1
> (mirror), or RAID level 5 (striped with parity distributed over components)
> are the obvious possibilities; what are the advantages and disadvantages of
> each?

In a nutshell:
  raid1: safe and (relatively) fast but not space effective.
          - safe against failure of 1 of the 2 disks
          - fast in read (can be distributed among drives), a write
            must be done twice...
          - You loose 50% of space
  raid5: safe and slower but more space effective
          - safe against failure of 1 of the N disks
          - slow in writes - must calculate check-sum
          - with 3 disks (the minimum!) you loose 30% of diskspace

I'd say you need raid1

Leo.