I hope you'll take the time to read this - and give it serious consideration ...
With a JBOD disk configuration, you get a single large "logical" volume, one disk with all your space - and as you write data to it, it stores it on the first physical disk, and then, when that's full, it'll use the second - very convenient, until a drive fails, or some other glitch occurs.
What you need to know is what happens when a drive fails - let's assume, for the purpose of this discussion, that you haven't filled the first physical disk yet, so ALL of your precious 900GB of data is stored there, and NONE on the second - if the second drive fails, you WILL LOSE ACCESS TO YOUR DATA, even though it's not on the failed drive.
Understand this very clearly - your data is at risk, just sitting there - whether or not you upgrade the firmware. If you value it, back it up NOW - you think it's impossible, consider what you'll do without it - it is YOUR data.
To answer your question - no - 1.08 should not request a re-format. It didn't when I upgraded.