I have an Envoy Pro Enclosure (OWCMAU3ENPCIECS / OWCMAU3ENPRPCIU) [w/ OEM SSD - 512GB Mid-2015 Macbook Pro Retina SSD] that I use as a bootable external MacOS installation and it works fine.

I have been unable to upgrade MacOS on this external drive (I can with other enclosures/SSDs). When I commence the upgrade process, the computer restarts the 1st time and starts 'upgrading' but when it restarts again it always defaults to the internal drive and the installation doesn't complete. I've set the startup drive in System Preferences to the external drive.

I think the drive isn't seen immediately at startup and this is causing the problem. The only option I can see now is reinserting the OEM SSD into the MacBook to upgrade and then reinserting it into the enclosure - a bit of a pain.

Is there some trick to upgrading the OS on this kind of enclosure? OWC went silent when asked...

  • To see if you can get the hardware to boot, you could use CCC to copy over a working system. bombich.com free 30day trial. – historystamp Jul 27 at 7:53
  • The hardware boots normally in a regular use scenario. It simply cannot complete a MacOS upgrade cycle. – Vaultnaemsae Jul 27 at 11:00
  • I tried a couple of things based on a blog post. It led me to recovery mode, reinstalling Mojave (doesn't erase any existing personal files/data), doing some checks in disk utility, and then a couple of terminal things before finally firmware locking the startup drive to external. I've now had various failure icons (prohibited sign / flashing folder with question mark) at startup and in the middle of the 10.14.6 update. I undid firmware lock and now I can run from the ext. disk again...still can't complete an OS update. dmoonc.com/posts/booting-macos-mojave-from-an-external-ssd – Vaultnaemsae Jul 28 at 18:12
  • This has proven essentially unsolvable. The only 'half solution' is to make a clone of the SSD on another drive, update it there and then reclone it back to the original. – Vaultnaemsae Aug 3 at 11:33
  • Give OWC a call. The one time I call them for support they were helpful. – historystamp Aug 3 at 18:29

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