Mac booting from internal and external drive

[phoenixmac]

Hi,

I have a MacBook Pro M3 and I have two installations, Local disk and external.

When there is an update on one, for example if I apply an update when I am booting from the external drive, then next time when I want to boot to my local drive, it won't let me boot from that OS. I then try to repair, and it does to allow me to do anything. I have gone through so many websites but cannot find anything. I end up reinstalling the local OS. The same happens on the local disk, If I install an update, I cannot boot from the external.

 

[EugenDoga]

Hey @phoenixmac

It sounds like you're experiencing quite the hassle with managing dual boot setups between your internal and external drives on your MacBook Pro M3. When updates are applied, it seems like the boot process gets disrupted, which isn't uncommon in setups where macOS runs from multiple drives.

Here are a few tips that might help stabilize your setup and prevent the need to reinstall the OS frequently:

1. Set the Default Startup Disk:
   • Make sure to set the default startup disk through System Preferences. Go to Apple Menu > System Preferences > Startup Disk, select your preferred startup disk, and click Restart. Doing this before and after updates might help maintain your choice of booting volume.
2. Use the Option Key for Boot Selection:
   • Whenever you start up your MacBook, hold down the Option (Alt) key immediately after turning on the device. This will bring up the boot manager, allowing you to select which drive to boot from (either internal or external). This can be particularly useful if your system does not boot from the intended drive automatically.
3. Check Disk Permissions and Integrity:
   • Use Disk Utility to check the integrity of both your internal and external drives. You can do this by booting into Recovery Mode (hold Command + R on startup), launching Disk Utility, selecting the drive, and clicking on First Aid. If there are any issues, Disk Utility might be able to resolve them.
4. Avoid Conflicting Software Updates:
   • If you frequently switch between the drives for booting, try to keep the software environment as similar as possible between them (especially in terms of major updates or system settings) to avoid conflicts.
5. Update Bootloader and Firmware:
   • Occasionally, the Mac's firmware might need an update, which is typically included with macOS updates. Ensure your machine's firmware is up to date by installing the latest macOS updates available for your model on both drives.
6. NVRAM Reset:
   • Resetting the NVRAM might help resolve issues where your Mac fails to remember your chosen startup disk. To reset NVRAM, turn off your MacBook, then turn it on and immediately hold down Option + Command + P + R for about 20 seconds.
7. Software Conflict Check:
   • Consider if any third-party software installed on one or both systems could be affecting the boot process. This is common with security software or tools that modify system-level functionality.

If these steps don't help and the issue continues, especially with updates messing up the boot order or accessibility, you might want to consider consulting with a professional or reaching out to Apple Support. Sometimes these issues can stem from deeper hardware interactions, especially with newer chipsets like the M3.

 

[phoenixmac]

This is exactly the problem

"Avoid Conflicting Software Updates:

• If you frequently switch between the drives for booting, try to keep the software environment as similar as possible between them (especially in terms of major updates or system settings) to avoid conflicts.

When updating the one, the other will not boot. When trying to keep them on the same version by updating it breaks the other.

 

[EugenDoga]

I see what you mean—that’s a tricky situation. Since keeping both systems synchronized still leads to issues, perhaps try staggering the updates. Update one drive and test its stability before updating the other. This might help identify what changes are causing the boot problems.

Also, consider making bootable clones of each drive before updates. If something goes wrong, you can revert quickly without a full reinstall.

Keep pushing, and maybe check some tech forums for similar experiences. Sometimes community solutions can be incredibly helpful. Hang in there!

 

[TonyAguila]

Hi,

I have a MacBook Pro M3 and I have two installations, Local disk and external.

When there is an update on one, for example if I apply an update when I am booting from the external drive, then next time when I want to boot to my local drive, it won't let me boot from that OS. I then try to repair, and it does to allow me to do anything. I have gone through so many websites but cannot find anything. I end up reinstalling the local OS. The same happens on the local disk, If I install an update, I cannot boot from the external.

I don’t have an M3 Mac yet, but I don’t think that’s the issue. Just to give you an idea of what I have to put up with, I have a Studio, two external NVMe drives, 4 terabytes each, and eight external Thunderbolt SCSI drives, mix of both hard and SSD drives. On the NVMe externals, I have an installation each of Monterey, Ventura, Sonoma (2 flavors, one a barebones installation of Sonoma, the other a virtual copy of my main internal drive. The two Sonoma drives are for testing beta versions of macOS, before I commit to updating my main system, depending on how stable the beta seems.

The best way I found to switch drives is to select the one you want to boot from with System Settings > General > Startup Disk. You should get a prompt to “authorize user(s),” enter their password(s). You will then get a secondary prompt for your admin password. Enter it and you should be able to restart. The drive selector from a cold boot (by pressing and holding the power button) never worked for me, probably because of the different macOS versions available.

Going back to your default system should be a similar procedure, although I had encountered instances of not being asked to authorize users before switching back. Still a mystery to me…

By the way, I recommend updating to Sonoma 14.5 (23F79). Best version yet!