One of the two 4TB WD Red drives in my NAS enclosure started giving I/O and S.M.A.R.T errors so I took it in to PBTech and they gave me a new one (Nice Warranty service incidentally).
The Drive has been running in the NAS 24/7 as half of an 8TB striped array since June 2015 (3yr warranty). I have a backup as per previous threads so no issue there.

So what I'm considering is should I put the new drive back into a striped array with the remaining old one which is the most convenient thing to do or is it a bad Idea given the age and wear difference between the 2 drives?
If I use them as separate volumes I have to split all my data up across the two which is a nuisance, I do prefer all the free space available in one place and find it much easier to manage.

Appreciate any advice or opinions please.