USB external hard drive is mounted on one MacBook Pro but not another I have a Hitachi rpm-5400 160GB hard drive in an Orico USB 3.0 hard drive case. The hard drive is formatted as ExFAT.




I plugged this drive on my Mid-2012 Non-Retina MacBook Pro and it mounts fine in both OS X El Capitan 10.11.6 and Windows 10. But when I plugged into my Mid-2014 Retina MacBook Pro running El Capitan 10.11.6 it doesn't mount. Saying the disk you inserted was not recognizable by this computer. It happens on both of the USB port on the Retina MBP.

I also tried this on a Late 2013 iMac also running El Capitan 10.11.6 and nothing happens. Not even the disk unrecognizable message. I opened Disk Utility app on the iMac, it didn't even show up.

I am pretty sure this problem is not with the drive, as the 2012 MBP mounted the drive fine. Where should I go next to fix this problem? I don't want to erase the drive because it have important informations on it and it takes very long time to copy it to another drive.

Thanks
My intuition would say that the drive might be drawing a little more power than the USB spec allows and one Mac can supply that power and the other cannot, but that's just speculation.

You would need to measure the voltage or try a different drive in the same enclosure with the same two Mac to start to pick apart why you get different results on two hardware setup.