Now High Sierra is released and not in beta, I'm wondering what the rules are about covering drives to APFS.
The release version of High Sierra auto converts SSDs to APFS on installation. But we know that Apple pulled the conversion of Fusion drives during the beta. We also know that non-fusion spinning disks can be converted to APFS but are not auto-converted.
According to the developer advice and several internet sources, other drives can be converted by using Disk Utility (right click the disk and the option will be greyed out if not available).
So I thought I'd try this on an old (late 2009) 27" iMac and the option was not available (the internal disk is actually new this year so it isn't just age). My Macbook Pro (early 2015) internal SSD converted automatically. Then I have some external disks all of which are perfectly functional. So I tried some of them. My Time Machine external disk would convert (not sure whether it is worth it) and old spinning 500GB spinning disk (extracted from an old MacBook) will convert. But two other disks (a LaCie 2GB USB and the original 1GB from my iMac) will not.
So what are the rules? Which disks can be converted to APFS? It is clearly more complicated that Apple's guidance which implies any HFS+ drive can be converted. Is it a settings thing we can manually alter, or is it a hardware thing we can't fix?