Hi, I held off updating my MacBook Pro (2015) to 10.13 until now. I'm currently running Sierra. I think I'm ready to update it to 10.13, but I just have a question. I know it'll convert my internal SSD to APFS, but are there steps I need to take for my backup drive? I have a Western Digital drive with Time Machine backups dating back at least a few years. I did a search, and found a thread here from back in September, but it didn't exactly answer my question. I know I'd have to convert the external drive to APFS myself, but my question is, do I have to? Can I keep the external on HFS, and then continue to use it to backup my MBP, which after the update will be APFS? I want to update for some software compatibility reasons, but I just don't want to mess up my backups in the process. Thanks.