iMac won't boot from USB disk after updates

[DN667]

I'm running my 2017 27" Retina iMac off an USB disk (due to a failed internal SSD). This works fine, however, after any update to the OS, the USB disk won't boot anymore (blinking folder fail at boot). The only fix seems to perform a clean install of MacOS (now on Ventura, latest) and restore everything else from TimeMachine. As this may happen a few times a week I'm getting pretty desperate.

Any clues on how to fix this, except for installing a new SSD? Thanks!

 

[Bigwaff]

Have you tried holding down Option/Alt during startup? You should get a dialog for picking a boot disk.

 

[DeltaMac]

No dialog on that Option-boot screen, just the normal Option-boot picker screen, letting you choose your boot drive, then press return to continue with the boot.
Once you are successfully booted, go to System Settings, then to General, then Startup Disk.
Make sure that your external boot drive is selected.
If that does not help, then you should expect that the fix will be to replace your external drive, as the one that you are using now may not be working properly. Sounds like you keep a good backup, which will make the task of moving to a different boot drive pretty simple - although if you have a more reliable drive then, you might then not have to do that restore as often. That might be a Good Thing™

And, thinking that your "failed internal SSD" might be causing some of your boot problems ("failed" does NOT mean that it is now invisible to your system), you should consider removing that internal drive, replacing that with a new SSD (prices continue to drop) - giving you back the performance that you used to have from your internal SSD boot drive.

 

[DN667]

Hello all,

Thanks for the suggestions.

* I've tried selecting my USB disk during boot. This however doesn't correct the issue; whilst the USB disk is visible to the system, the Mac doesn't consider it as bootable.
* The USB disk is set as default boot disk, which works fine.
* The internal SSD is dead as can be, MacOS doesn't even list the SSD anymore.
* I don't expect my USB disk to be faulty as it works like to a charm, except for after an update to MacOS. I'm not sure how MacOS works in this regard, but if this were a Linux system I'd argue that updating the boot partition failed after updating the kernel (or likewise).
* I'll replace the SSD eventually, but as it's quite involved process I opted for using USB instead.

Thx!

 

[Fishrrman]

Questions and thoughts...

Is the "USB disk" an SSD or a platter-based hard drive?
(if it's an HDD, get an SSD instead)

Is the USB disk a "pre-packaged" disk or did you put it together yourself?
(if the latter, try a different enclosure)

 

[DN667]

My USB disk is a new Sandisk Extreme Portable SSD V2 PRO (2TB). So yes, it's prepackaged

 

[Fishrrman]

I've always liked Sandisk products, but I've heard of possible problems with the "Extreme" SSDs and Macs. Might be firmware, or something else...