We're finally in the home straight - we've tested RAID 0, RAID 1, RAID 10 and RAID 3. There's only RAID 5 left. Like RAID 3, one disk's worth of space is reserved for recovering from a failure, but where RAID 3 stores the parity information on one disk, RAID 5 distributes the parity across all the disks. Again, 3, 5 and 9 disks are possible sweet spot configurations, and we're looking out for any write penalties caused by parity storage and calculation.
With a three disk RAID 5 array, ATTO shows us:
Thankfully, the 3 disk RAID 5 set shows performance akin to the 2 disk RAID 0 set. There are scenarios where it could be faster; but there are also scenarios where it should be a lot slower. Let’s see what HDTach has to say about the 3 disk RAID 5 set:
There are a couple of unexpected dips in performance, but nothing particularly worrying. HDTune then, to see the difference between sequential and random access:
If it weren't for the tag in the top left, identifying this as a RAID 5 set, you'd be forgiven for thinking this was a RAID 3 set or the 2 disk RAID 0 set.
There is no hope for random IO.
