Booting from external drive and can't format internal drive

[ethant]

Greetings.


I have a Mac Mini (running 10.13.6) that is quite slow. It's not my primary Mac so it doesn't need to be a speed demon, but I decided to try cloning the slow spinning drive to an external SSD and booting from that to speed things up. I used Carbon Copy Cloner to clone the drive, including the recovery partition, and set it to boot from the external SSD.

I am pleased to report that the performance is much improved, certainly good enough for what I use this machine for. Now the problem I am running into is that I would like to wipe the internal drive and use it for storage. But no matter what I try, I can't seem to make this work. I first tried in Disk Utility and got an error that the drive can't be unmounted. I also cannot partition the drive.

I did some Googling and based on that tried various things in terminal, including force unmount, reverting from CoreStorage on the internal drive, etc. and nothing works.

Something else disconcerting is that I don't seem to be able to boot into recovery. I figured I would try formatting the drive there, but after rebooting with CMD-R I just got a black screen for a long time. I eventually power cycled the Mini to boot it up normally. Not sure if this is because there are two recovery partitions (the original on the internal drive, and the cloned one on the SSD)?


Any help would be appreciated! Here is the output from diskutil list for your reference:


Mac-Mini:~ es$ diskutil list

/dev/disk0 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *1.0 TB disk0

1: EFI EFI 209.7 MB disk0s1

2: Apple_HFS Data Store HD 999.3 GB disk0s2

3: Apple_Boot Recovery HD 650.0 MB disk0s3


/dev/disk1 (external, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *500.1 GB disk1

1: EFI EFI 209.7 MB disk1s1

2: Apple_HFS Macintosh SSD 499.1 GB disk1s2

3: Apple_Boot Recovery HD 650.0 MB disk1s3

 

[Fishrrman]

Try this (no promises):

1. Power down, all the way off
2. Press the power on button and immediately hold down the option key until the startup manager appears
3. You should now see both the internal and external drives as selectable boot devices
4. Click the external SSD with the pointer, then...
5. Hit return and IMMEDIATELY hold down the shift key and keep holding it down
6. This should get you booted up from the external SSD into "safe mode"
7. Once you're in the finder, open Disk Utility
8. Look towards DU's upper-left-hand corner. There's a small popup menu, and when you click it, you should see the option to "show all devices". Is it there?
9. If so, choose that option and now select the "topmost" representation of your internal drive (which should be the physical drive itself).
10. Can you now click the erase button and erase it?

 

[ethant]

Thanks for the suggestion Fishrrman. I actually ended up selling that mini and getting the 2018, so I can't try it out unfortunately.

Try this (no promises):

1. Power down, all the way off
2. Press the power on button and immediately hold down the option key until the startup manager appears
3. You should now see both the internal and external drives as selectable boot devices
4. Click the external SSD with the pointer, then...
5. Hit return and IMMEDIATELY hold down the shift key and keep holding it down
6. This should get you booted up from the external SSD into "safe mode"
7. Once you're in the finder, open Disk Utility
8. Look towards DU's upper-left-hand corner. There's a small popup menu, and when you click it, you should see the option to "show all devices". Is it there?
9. If so, choose that option and now select the "topmost" representation of your internal drive (which should be the physical drive itself).
10. Can you now click the erase button and erase it?