Question: Disk Utility cannot unmount disk, despite booting from a different disk.
I'm running a Mac Pro 12 core with Snow Leopard. I have two start up disks, an SSD and a 4 TB SATA. Upon start up with either disk I can do one or two simple things opening a disk, emptying the trash... small things like this) before I get the BBOD... When I try verifying the 4TB disk, I get a couple of errors, and a notice to repair the disk. When I try to repair the disk, it says the disk cannot be unmounted. I've booted from my SSD, but can't get the 4TB to unmount so I can repair it with Disk Utility.
MacBook Pro, iOS 6.1.6, 10.6.8 OS