I bought a 1tb usb 3.0 drive for time machine backups. Backed up my MBA, my wife's Mac Mini and my Mac Mini. I lost the ability to connect to wifi on my Mac Mini and after trying to fix the problem without success, I figured well just do a restore. I did. The restore somehow took my wifes setup and put it on my machine. When I looked on the 1tb drive I saw that my backup was listed but it wasn't used. Don't believe them when they say that Yosemite can use the same hard drive for all your machines and time machine will keep things separate. Luckily, its a pretty new machine and I did save all created info to a thumb drive. But what a pain. I'm putting a fresh copy of Yosemite on now.. only 2 hours and 48 minutes to go.