I have reset PRAM and SMC and it still happens.

This wasn't an issue before the upgrade to Big Sur, and it is still an issue after the full recovery of my Catalina backup. Whenever the backup drive is attached at power up the computer seems to get confused during boot and ends up in recovery mode. Even holding Option at power one selection the bootable drive doesn’t work.

I have made sure the Start Up disk is set properly to the T3 SSD and it still does not boot properly if the backup disk is attached. Once it is booted I can connect the backup drive and all works as expected. I tried restarting without the 4TB backup drive connected and it worked (I wish I would have tried this after the upgrade to Big Sur). On Sunday I reinstalled from a backup from before the upgrade and guess what, it still booted to recovery. I tried everything (well almost everything as I leaned today, keep reading ) and I couldn’t get Big Sur to boot normally. Saturday morning I upgraded to Big Sur and after it was done, I found the system had booted to recovery mode. After upgrade to Big Sur iMac does not boot correctly and boots to recovery when external drive with time machine backups is connected 2014 21.5” iMacĬatalina OS 10.15.7 is on external 500Gb Samsung T3 SSD (has been for years)Įxternal 4TB Western Digital for Mac’s local backup as well as a network backup drive for other MacBooks on the network (has been working perfectly for over a year)

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