Yes but Apple clearly doesn't want it as a default boot drive for hard drives and fusion drives just yet. There has to be a reason.
I never said they do want it to be default for HDDs, nor that it should. It's just that APFS was designed and optimized for SSDs primarily. And the reason behind their reluctance to make it default also on HDDs could very well be that they just haven't spent enough time testing it on HDDs themselves plus they lack meaningful user data from the real world, too. That may have been either intentional or just a result of time constraint. It is strange though, that you are/you will be able to use APFS even on external HDDs. If you do not intend it to be the default filesystem also on HDDs machines at some point, then why not just make it SSD-exclusive? I guess time will tell.
But I can't say I'm trying to push to get my Mac 3,1 with a Fusion Boot drive (and a SoftRAID array) up and running on APFS anytime soon.
I on the other hand look forward to it. HFS+ is old, has many shortcomings and it's definitely not the way to go forward. Something like APFS was inevitable, I'm surprised it took them this long (not to play down the amount of work that goes into creating a whole new filesystem, and one that has to run on many different devices, from desktops, through tablets and phones, to watches). APFS has many perks I'm excited about. It's not all rainbows and unicorns, though. I'm very disappointed there's no real data integrity (checksums on user-data, not just APFS's own metadata), something akin to ZFS.
I do have faith, though. Like you said, what we've seen with iOS/tvOS have been promising. Converting millions of iPhones to APFS with the update to iOS 10.3 went smooth and without problems. That's a big achievement. Fun fact, they have been actually silently converting our iPhones to APFS and then
back to HFS(X) during several iOS updates prior to 10.3. This gave them confidence they can really do that at scale with 10.3.
Anyway, I'm happy to discuss it more, but please PM me if you have more thoughts. I don't want to turn this thread into a conversation about APFS, it's not what it's for
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