I have a Seagate slim USB drive (no external power required) attached to my desktop iMac and use Time Machine (and TimeMachineEditor) for desktop backups. It's interesting, in the 15 years that I've own Mac-based computers, I've never had to refer to files on my TM backup. (but I know that the day after I were to stop using it, I'd have a vital need for it

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On my second iMac that serves as a Plex server, I have an 8TB external drive as the primary media drive. I have two additional 8TB drives that serve as backups to that primary drive, which I perform periodic backups in an alternating fashion using the "Sync Folders" app.