You may know that you can connect a USB thumb drive or an external HDD to your Apple Airport Extreme router. This is useful for file sharing or Time Machine backups. But if you have a spare internal HDD you can make this work as a network drive, too - with a powered USB to SATA adapter. My config: - Apple Airport Extreme 802.11ac (ME918Z/A) router - i-tec powered USB 3.0 to SATA adapter - Seagate 3TB Seagete NAS Series 3,5" HDD For the adapter and HDD you can use any similar parts of course.. e.x. Anker Powered USB 3.0 to Sata Adapter or a 10TB HDD if you'd like to. Preparing the disk for Time Machine backups is simple.. Just attach the HDD with the adapter to a free USB port on your computer, and format the drive in Disk Utility as format: Mac OS X Extended (Journaled), scheme: GUID, name: BackUp for example. Now attach the HDD with the adapter to your AirPort Extreme router and that's it! The Time Machine setup process is the same as for any network connected disk. Make sure you enable file sharing in Airport Utility. I also clicked Secure Shared Disks with: Device password. To enable the disk as a Time Machine backup destination, Open System Preferences / Time Machine / Select Disk.. and simply select the disk, mine listed as: "BackUp on Airport Extreme". Advantages: - You can have a larger capacity backup solution than the Airport Time Capsule (only 2TB and 3TB options are available by Apple) - If the HDD is not in use (99% of time when it's not doing backups) it turns off so it doesn't consume electricity and first of all it increases HDD lifetime. - Network backups can be used as local backup disks if you disconnect the drive from the router. - Much more easier to replace the disk if you're low on free space or the HDD is failing. For a Time Capsule router you need to disassemble the whole thing to replace the built in HDD.