Mac pro won't startup when external drives are "on".

[iHanuka]

Hello,
I am using a mac pro 2008 with a Mercury Accelsior E2 PCI express with an internal Solid State Drive on the card and 2 external SSD drives.
I am using Mac Os X El Capitan and it's installed on the SSD that is physically on the card. and this is the startup disk.
When the external drives are "OFF" the computer starts up just fun.
But, When the 2 external drives are "on" the computer won't startup, as if it can't find the startup disk.
So I can't leave them on.
Any ideas?

 

[adam9c1]

Totally wipe the external drives (using a different computer). Then plug in to your tower.

 

[crjackson2134]

Hello,
I am using a mac pro 2008 with a Mercury Accelsior E2 PCI express with an internal Solid State Drive on the card and 2 external SSD drives.
I am using Mac Os X El Capitan and it's installed on the SSD that is physically on the card. and this is the startup disk.
When the external drives are "OFF" the computer starts up just fun.
But, When the 2 external drives are "on" the computer won't startup, as if it can't find the startup disk.
So I can't leave them on.
Any ideas?

This happens sometimes with PCIe drives. They lose their startup disk settings after a PRAM and/or SMC reset. Sometimes after an extended power loss too.

Try going into your settings > Startup Disk > Select the PCIe drive you want.

That may or may not fix your problem. It does for me...

On first boot with ALL external drives attached and powered on, try holding the option key as you power it on. Continue to hold it down from the time you hit the power button, until you see all the boot options. You should be able to select your desired drive and boot. If that works, then selecting the same drive from the startup drive settings outlined above should fix your problem..

Hope this is the issue, and fixes your problem. Good luck.