I recently received a tech support call from a customer wondering how to attach an external hard drive to their Time Capsule to expand their storage capability. It is a very simple process to do.
You’ll first need to format the disk as Mac OS Extended if you’re on a Mac or as FAT32 if you’re running Windows. You’ll need to do the formatting from your computer as the AirPort Utility doesn’t support formatting external disks.
Step two is to plug it into the USB port on the back of your Time Capsule. You can also plug in a powered USB hub into that port and gain multiple connections into your Time Capsule.
Step three, launch the AirPort Utility, click on your Time Capsule, then enter your devices password. You should see an icon on the top of the window called Disks. If you click on that you can set access privileges for that external drive.
Your drive should now show up in finder as a shared network volume.