Startup confusion

[blackxacto]

17,1 iMac, 10.12.6, I have two external backup drives. 1 external drive has a bootable partition w 10.12.6. Somehow my iMac decides to restart from this external partition, rather than my main Sierra fusion drive. How can I remind the iMac to start from its fusion drive, rather than this external partition without holding OPTION.

It's like the iMac has forgotten what is the main hard drive.

 

[Taz Mangus]

17,1 iMac, 10.12.6, I have two external backup drives. 1 external drive has a bootable partition w 10.12.6. Somehow my iMac decides to restart from this external partition, rather than my main Sierra fusion drive. How can I remind the iMac to start from its fusion drive, rather than this external partition without holding OPTION.

It's like the iMac has forgotten what is the main hard drive.

Go into System Preferences->Start Disk and select the Fusion drive.

 

[blackxacto]

Thank you very much. I remember now. I used to do this in System 9 and such, years ago. How soon I forget.