I'm trying to backup my new MacBook Pro (2015) to my old MacBook Pro (2011) using OS X Server. I have a Seagate backup plus slim 2TB external hard drive hooked up to the old MBP, which is where I want to backup my new MBP to using Time Machine. If I select an internal folder to backup to on the old MBP through OS X Server, everything works fine and the backup is successful. But if I try to add the external HD to the list of backup destinations in the server, I can't. I click "Browse", select the hard drive, and then click create. But when I click create, nothing happens no matter how many times I click it. Though when I click create and the destination isn't external, then the destination is added. The external HD has been reformatted so I can write to it on a Mac. I'm really at a loss here why I can't add the external HD to the destination list and would appreciate any advice.