OS X Yosemite: Disks you can use with Time Machine
You can use Time Machine with a Time Capsule, and with USB, FireWire, and Thunderbolt disks. The disk can be directly connected to your Mac or be on a network. If a disk has partitions, you can use one of the partitions for your backup disk.
Time Machine can’t back up to an iPod, iPad, or iPhone, or a disk formatted for Windows. If you connect a disk formatted for Windows, it can be reformatted (permanently removing all data) to a Mac filesystem format and used as a backup disk.
The most common format for a Time Machine backup disk is Mac OS Extended (Journaled) format, but Time Machine also supports Mac OS Extended (Case-sensitive, Journaled), Mac OS Extended (Case-sensitive, Journaled, Encrypted), and Xsan formats.
If the disk using the Master Boot Record (MBR) partition type, some partitions may not be available for use with Time Machine.
If your backup disk is on a network, the network server must use Apple File Protocol (AFP) file sharing, and both your Mac and the networked backup disk should have Mac OS X v10.5.6 or later. The AFP disk must also be “mounted” (available to your Mac) during the set up of Time Machine. After you select the network disk in Time Machine preferences as a backup disk, Time Machine automatically mounts the disk when it’s time to backup or restore your data.