Attaching NAS to Time Capsule and backing up Mac to NAS using Time Machine

I forgot to mention in my cautions above that the USB port on the Time Capsule and other AirPorts is underpowered....(it was originally designed to support a printer).......so you often need to use a powered USB hub with an external drive connected to the USB port on the AirPort.......even if the external drive has its own power supply.

Time Machine backs up differently to a USB drive connected to a computer......(this is called a "local" drive)......than it does to "network" drive attached to an AirPort router.

So, the backups that you have made with the USB drive will not be useable if you try to connect the USB drive to the Time Capsule and back up that way. Time Machine will start all over again with a new complete backup of your Mac.

Not sure how much time you want to spend trying to do something that I do not recommend, but if you want to pursue this, the first step would be to connect the USB drive to the Time Capsule and then see if the drive appears when you open up AirPort Utility, click Edit and then click the Disks tab at the top of the window.

When you do this, you will see the Time Capsule drive......(named "Data", unless you have changed the name of the drive)......along with the name of the Seagate drive.

If the Seagate drive does not appear when you do this, then the next step would be to try using a powered USB hub to see if things will work that way.

In theory, things should work. Of course, "should" is not the same as "will" in the computer world. But.....there are some downsides......

If the Time Capsule fails, then so too will any drive that is connected to the USB port on the Time Capsule, so you might want to think about that before you attempt to make any changes.

The USB port on a Time Capsule acts differently than a USB port on a computer, so if you have been backing up using the Time Capsule USB port, you may not be able to switch the Seagate drive over to your Mac and have things continue to work seamlessly.....or......vice versa.

You might also not be aware that the USB port on the Time Capsule is an ancient USB 2.0 design that is 2-3 times slower than a normal USB port on a Mac, so backups........if they work.....will take 2-3 times longer than normal.

Even if the Time Capsule might be working OK now, I would not recommend that you connect the Seagate drive.....or any other drive for that matter......to the Time Capsule to try to back up that way.