External drives won't mount on restart

One of my staff just got a new Mac mini with the USB 3 ports and Mavericks. It has 2 Seagate GoFlex 3TB hard drives connected: 1 for Time Machine, the other for Dropbox files.

When the computer is restarted, the drives don't mount. They are not visible in Disk Utilities. Unplugging the drives and plugging them back in will mount them. I'd like everything to mount and Dropbox to start up automatically for this user, which worked on the old Mac mini she was using. Now she has to go through multiple steps every time she restarts, which is not ideal.

Any ideas what might be causing this behavior?

Solution 1:

Open a terminal window and enter the following command:

sudo defaults write /Library/Preferences/SystemConfiguration/autodiskmount AutomountDisksWithoutUserLogin -bool YES

That will prevent macOS X Lion, Mavericks and Yosemite from un-mounting drives at logout. Maybe that's the problem you're seeing as well.