Can I sanity check something?

I've got a cluster in a box - in the form of a 2240-4. Single shelf, but it's got 4 SSDs installed. 

Which works as two per head. 

Looking at it, I can't actually configure a hybrid aggregate, because I have to match RAID types (RAID-DP on two drives doesn't work). That's on my current code rev of 8.1.3

Upgrading to 8.2 might be a solution, because then I could RAID4 my SSDs.

But I'm wondering - what happens, given a system with no spares, one of the SSDs dies? (Or indeed, whether running with no spares is actually a good idea in the first place - I do have spares for my SAS drives, but not SSDs).

With that in mind - am I onto a bit of a loser here? And I should just be looking to replace my SSDs with some drives to match what I've got already?

Or perhaps have one head with flashpool, 3 drives + spare and one without?