I'm currently running Sierra on a late 2009 Mac Mini with an SSD. My backup drive is split between Time Machine and Carbon Copy Cloner. It's about time to get a new Mac Mini which will come with High Sierra or if I wait a while with Mohave. I won't be able to afford an upgrade to an SSD, sadly. So my first question is will either OS use AFS or is that only for hard drives that are SSDs. If AFS is used, will I have problems transferring all my documents etc from Time Machine which uses the old format? And also, can I upgrade the Time Machine partition to AFS without losing all my backup history? Many thanks.