Deleting Old User ID off my Mac mini 2018 HD

den.thed wrote:

I would erase and reinstall the macOS on the internal drive, then set it up with the new user name to fall back on if and when there is a problem with the external startup drive.

Well, there IS a reason to keep macOS installed on the internal drive ... as well as the original (admin) user account. That account is the "Owner" of the machine. Ownership is a relatively new macOS concept (not well documented, either). You were able to install macOS on the external drive because you were using the Owner account. In theory Ownership privileges are copied to the new admin account on the external drive, but that is not always the case (users have found out the hard way). It would be prudent to keep the old user account intact. Just delete whatever user data you no longer need to keep on the internal drive.

BTW, you can still use the internal drive for data storage when booted from the external drive.

As I understand your question, you created an external startup drive, it's working well, and now you want to repurpose the internal drive — formerly used as the Mini's startup device — for either general storage or other purposes because you do not intend to use it as a startup drive ever again.

Yes you can do that, but having rephrased the question in that manner might cause you to reconsider that action.

Use Disk Utility to erase the Mini's internal storage.

Erase and reinstall macOS on the internal drive.

Use Disk Utility to erase an Intel-based Mac - Apple Support

Stephen Altobello1 wrote:

Are you suggesting that it's not smart to repurpose the internal drive?

I was and I would not repurpose the internal drive as a blank storage drive.

I would erase and reinstall the macOS on the internal drive, then set it up with the new user name to fall back on if and when there is a problem with the external startup drive.

I used to partition my boot drives ... when my Macs had HDDs and used HFS+ ... in order to, as you said, isolate user data from the OS. It yielded better performance because the system & apps were kept in the faster (outer) area of the HDD. With APFS and SSDs all that has changed.

Partitioning was never a risk-free proposition and there are increased risks partitioning an APFS boot drive due to the complexity of APFS and the way it and macOS have continued to evolve (significantly) with each new release since High Sierra. The container & volume structure has gotten increasingly complex to the point where now the internal system drive comes with three containers (two of which are hidden) & 6 volumes (four of which are hidden). While that in itself isn't a problem, any user misstep could corrupt the system.

You can certainly do that. Once repurposed in the manner you propose it just can't be used as a startup device.

MartinR wrote:

I'll add that after reinstalling macOS on the internal drive, you can still use it for data storage when booted from the external drive.

True! I was going to add that depending on the OP's response.

What do you think..? Would that data storage be better in a separate partition or in a separate APFS volume..?

den.thed wrote:

What do you think..? Would that data storage be better in a separate partition or in a separate APFS volume..?

Neither would really be necessary. But it may be advantageous to create a separate Volume specifically for user data storage ... just to keep things as orderly as possible.

Partitioning an APFS boot drive is a dangerous thing to do and I do not suggest it.

MartinR wrote:

Partitioning an APFS boot drive is a dangerous thing to do and I do not suggest it.

I have been creating partitions, i.e. containers, on boot drives since APFS came out without any issue. However, lately I have moved to simply creating volume groups since the space can be dynamically allocated instead of having fixed size partitions.

I have done both separate containers or volume groups for simply isolating data from the OS and also for dual booting (mostly the latter). I no instance have I found anything "dangerous" in doing so.

Thank you!