Mac won't reboot with external drive connected

[Jigga Beef]

Mac won't reboot with the external drive connected

I have Mac Pro running High Sierra
When i have a USB drive plugged in with a cloned boot drive (which i cloned with CCC) my mac won't boot up.

The Start-Up disk is selected properly

Assuming there's a setting I'm missing but can't figure it out.

 

[Jigga Beef]

bump!

 

[Fishrrman]

Are you saying it won't "boot from the clone"?
Or are you saying it won't boot AT ALL?

Have you tried booting with the option key held down (until the startup manager appears)?
Then, select the external drive with the pointer and hit return.

If it won't boot from the clone, I'd try this:
1. Use Disk Utility to ERASE the cloned backup. NUKE IT BACK TO ZERO -- Mac OS extended with journaling enabled.
2. Use CCC to repeat the cloned backup -- all over again (yes, I realize this will take some time).
3. Try to boot from it again.

Additional questions:
Who made the external drive?
How old is it?
Are you connecting "through a USB hub", or is the drive plugged directly into the Mac?

There are -some- USB external drives that may not be capable of booting the Mac. This is usually due to the drive controller board -- doesn't have anything to do with the OS on the drive.

There are some older Macs that won't boot from USB at all.

 

[Jigga Beef]

Are you saying it won't "boot from the clone"?
Or are you saying it won't boot AT ALL?

Have you tried booting with the option key held down (until the startup manager appears)?
Then, select the external drive with the pointer and hit return.

If it won't boot from the clone, I'd try this:
1. Use Disk Utility to ERASE the cloned backup. NUKE IT BACK TO ZERO -- Mac OS extended with journaling enabled.
2. Use CCC to repeat the cloned backup -- all over again (yes, I realize this will take some time).
3. Try to boot from it again.

Additional questions:
Who made the external drive?
How old is it?
Are you connecting "through a USB hub", or is the drive plugged directly into the Mac?

There are -some- USB external drives that may not be capable of booting the Mac. This is usually due to the drive controller board -- doesn't have anything to do with the OS on the drive.

There are some older Macs that won't boot from USB at all.

Sorry, I should have been more clear. It won't boot at all with the drive plugged in. I don't want it to be boot from the clone drive but the internal drive that works when the USB drive isn't plugged in. Its a WD My Passport.

 

[DeltaMac]

So - only that WD external drive, and any other drive (or other USB devices) attached doesn't affect booting at all?

What happens if you simply let the Mac try to boot with the WD drive attached? Give it 10 minutes, minimum.
Do you ever see the normal Apple icon, or see a blinking folder, or the "prohibited" symbol (circle crossed with diagonal line) - or anything at all appears on the display? Or nothing whatsoever, and the LED on the front of your Mac Pro flashes in

Finally, is the WD plugged directly in to a rear USB port, or is it plugged in to an external USB hub?