I've searched the forums and the web but could not find a definitive answer to this issue. When I upgraded to 10.11 none of my external disk drives would mount reliably. If I did get them to mount, RipIt failed to work as did MDRP. The drive works fine in 10.10 on another rMac so I doubt it i star drive. I think there is some software conflict but cannot figure it out. In the interim I downgraded to Yosemite but would love to get a solution. Adding to the confusion is when I upgraded my machine hung and I had to reinstall 10.11 from Restore.