Chosen Solution
MacBook Pro mid-2012 15" I just upgraded my 1Tb SSHD to a 2Tb SSHD. Trying to clone the drive never worked (that’s a different story), so I did a clean install of macOS Sierra. I was running El Capitan before. I put the old 1Tb SSHD in an external USB case and plugged it in. The light on the external case blinks frantically… for days, but the drive never mounts and is not visible in Disk Utility. I can unplug it and plug it into a Linux box which mounts it immediately. I thought I’d just copy from the old drive to a USB thumb drive on the Linux box. I can copy files to the thumb drive, but when I insert the thumb drive into the MacBook… nothing. It has no light to blink, so I don’t know if the MacBook is trying to read it, but I’ve tried removing and reinserting several times with the same result. Also not visible in Disk Utility. Back to the Linux box, where it mounts instantly. Both the USB thumb drive and the external case worked fine under El Capitan on this same machine. Any ideas?
If you have a 1TB, it likely can’t be powered by a single USB port. You may need to get a special USB cable that injects power from the other USB port, or if your enclosure has a power cable jack, get a matching USB to power cable.
