I want to connect an external Hard-drive (1TB) to my Raspberry Pi. However I want to do the following:

1) Partition 500GB for backing-up using "Time Machine"

2) Partition 250GB for general use for the Raspberry Pi

3) Partition 256GB for back-up of the Raspberry Pi and it's contents

I know how to partition the Hard-Drive but my question is this: Is it possible to have Time-Machine backing up to the External Hard-drive that is connected to the Raspberry Pi through SSH? I.e. The Pi has an IP address, both internal and external. What I want to end up doing is for my main desktop, it will use the internal IP because it is always connected to the network, however, my laptop will use the external IP to back-up. Is this possible? Thank you