I wish to upgrade m Macs to High Sierra. (I thin it's time).. However, although i have my NAS which houses all my data, i have few external drives and flash drives that are HFS+ hat i'd like to convert via Disk Utility afterward via the menu.. However, how safe if this method vs formatting as AFPS ? While you could always say "there is always a possibly of data loss while data stays on device and its probably recommended to reformat", how effective is this conversion from HFS +to AFPS+ on 2TB volumes and above? Has anyone does this and 100% success?