Follow-Up to My Recent Hard Drive Issue

Hi everyone. It has recently come to my attention that the issue with my external drive wasn't quite a hard-drive failure afaik, but the drive does need to be re-formatted. Actually now that I think about it, the thing might not have been formatted correctly when I got it in June of 2016. I didn't think to check back then or have anyone else do so, because I thought the thing would automatically detect which kind of computer I had. But that apparently wasn't the case. So my tutor is just going to try and do it himself tomorrow. He is sighted and honestly a bit impatient with some things, so I didn't even bother checking whether this process works with VoiceOver, lol. I already know how to do it because I checked earlier today with the A-Lady. But having said all that here is my question. Which music format should I choose when re-importing all my CDs? Or is there a way to just retain all my music during the process of re-formatting? Tia for anyone's assistance with this.