Setting up my dual docking station with two HDDs for Time Machine has me baffled.

I was told to format the TM HDDs, backing up my iMac running Big Sur, as Mac OS Extended (journaled) which I did.

I did this two hours ago using Disk Utility and got my dual dock system up and working just fine, or so I thought.

I was checking out one of the eclecticlightcompany.com’s neat little apps called Mints, chose to check Get Volume Info, and was surprised to see that both the HDDs I had set up two hours ago as Mac OS Extended (journaled) were now formatted as APFS (Case-sensitive).

Why is this happening? Should I be concerned? Should I reformat these HDD and if so, what format?

  • It used to be that Time Machine required HFS+. Perhaps you have discovered that under BigSur it requires APFS and will convert a filesystem as needed? Dec 2, 2020 at 20:47
  • Big Sur can use APFS Time Machine drives, but i can't find anything to say what it might do unrequested - eclecticlight.co/2020/06/29/…
    – Tetsujin
    Dec 3, 2020 at 8:34

1 Answer 1


Thanks you two for replying. I continued to research the subject and now realize that Apple automatically changes your external HDDs to an APFS format without a "by your leave".
That said, what I find odd is that instead of just changing them to APFS, Apple changed them to APFS (Case-sensitive). Truly strange, that.

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