What did I do wrong in Disk Utility (and how do I fix it)..?

[Anais Ninja]

This is a bit confusing, please bear with me.

About six months ago, I bought a Mac Mini, and am using an EXTERNAL drive as my Startup Disk.

I named the external drive Mac XD, and everything works fine.

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BUT when I use Disk Utility, my external boot drive seems to have a mystery partition...?

This mystery partition, called “Mac XD”, says that it's a “snapshot”, and does NOT mount on my Desktop...

THIS partition, called “ThisOne”, has all of my documents and files.
But it mounts on my Desktop with the name “Mac XD”, NOT “ThisOne”:

I DO remember entering the name “ThisOne” at some point while setting up the drive, but I cannot recall when or why.

I'd like to delete the “snapshot” partition without losing anything on the “ThisOne” partition.

What do I need to do here?

Many thanks in advance!!!

 

[gilby101]

What do I need to do here?

Nothing.

Taking your second screenshot first:

"Mac XD" (as viewed by Finder, etc.) is what Disk Utility shows as "Mac XD volumes". It is a combination of a read-only volume "Mac XD" and read-write volume "ThisOne". The separation guarantees that macOS itself can't be tampered with and is the same for everyone. But this is all hidden by Finder (and Open/Save dialogs) and you just see "Mac XD" and its folders. Your files (and all the changeable system files) live on the read-write volume "ThisOne", but are presented as being inside the combined "Mac XD".

In your screenshot the double ended arrow should link "Mac XD" on the desktop to "Mac XD volumes" in Disk Utility. When you drill down into desktops "Mac XD" you will see read-only operating system files as well as your data and added applications.

Normally your "ThisOne" would be called "Mac XD - Data". I don't know when you entered that, but if there are no problems, I would not worry. The name is odd, but the volume structures are correct.

Now the snapshot: during macOS install or upgrade, the install/upgrade process creates a new snapshot along side the previous version of macOS. This allows fall back to the previous state in event of any upgrade issues. Assuming the install/upgrade completes successfully the new snapshot "Mac XD snapshot" becomes the read-only volume that boots.

 

[Bigwaff]

You can't delete that snapshot nor should you. That "startup" snapshot is the Signed System Volume. In layman terms, it is the operating system files securely encrypted so they can verified as having not been tampered with. Your Disk Utility device tree looks normal.

 

[Anais Ninja]

Normally your "ThisOne" would be called "Mac XD - Data". I don't know when you entered that, but if there are no problems, I would not worry. The name is odd, but the volume structures are correct.

Now the snapshot: during macOS install or upgrade, the install/upgrade process creates a new snapshot along side the previous version of macOS. This allows fall back to the previous state in event of any upgrade issues. Assuming the install/upgrade completes successfully the new snapshot "Mac XD snapshot" becomes the read-only volume that boots.

Many thanks for the clear and detailed explanation, gilby101 - I truly appreciate it!
Thanks also to Bigwaff!