Same result.īefore I take the time to wipe the external drive and try a clean install (then restore all my stuff), anyone know what's going on?Įrror creating a macOS Big Sur bootable installer I am trying to create a bootable installer for macOS Big Sur on an M1 MacBook Air to use on a 2016 MacBook Air that cannot reinstall macOS in recovery mode. I ran the installer again - it only took a few minutes and again showed 'success' and a restart prompt. I can tell the install did write to the external drive but I suppose it didn't finish. In the Startup Disk pref pane, the external drive is selectable but it still shows as a Sierra boot. I went to the Startup Disk pref pane and made sure the external was selected and tried again. When I restarted, it booted from the internal drive instead. It took about 25 minutes and gave a 'success' message, prompting me to restart to finish. I downloaded the installer from the App Store and ran it to install on the external drive. The internal is a clone of the external just for backup, cloned via SuperDuper.Īccording to I can update directly to Mojave on this Mac Mini. The external drive has Sierra and this is what I always boot from. Mojave installation unbootable on external drive I have a Mac Mini (late 2014) with its stock internal drive and an external SSD via USB. Click Continue again, same thing happens, again and again.ĭoes anyone know how to make this work, preferably on the flash drive?

But when I reboot and select this partition to boot from by clicking the Continue button under it, I see a spinning progress indicator for 2 seconds, and then the Continue button becomes enabled again and no startup occurs.

Disk Utility indicates that this partition is now a APFS Volume Group with macOS 11.6, as expected. It seemed to proceed OK, completing after an hour or so. Might be slow I suppose, but since no luck on the flash drive I gave this a try. Third try: The installer indicated it was possible to do its thing on a second partition of my connected Time Machine spinning disk. Now the installer gives a different reason: Cannot install to this volume because the computer is missing a firmware partition. Second try: I erased and reformatted the second flash drive to Mac OS Extended (Journaled). But the installer said: The disk can't be used to start up your computer. I downloaded 'Install macOS Big Sur' and made a bootable installer of the first flash drive.įirst try: I booted from the bootable installer and tried to install Big Sur on the second flash drive. So I got two 16 GB USB-A flash drives and plugged them into a USB-3 hub which is connected to my Anker USB-C dongle. However I need to do some stuff (run Xcode 12) which requires macOS 11, not 12. My late 2020 MacBook Air with Apple Silicon is running macOS 12 Beta.

Mac os big sur flash drive