Having a very large external disk I wanted to limit Time Machine to use only part of it.
To do so - you can use the same technology as time capsule does - sparseimages.
In the following:
HOSTNAME is the result of:
hostname -s
MAC is the mac address of the network adapter:
ifconfig en0 | grep ether | sed -e "s/.*ether //" | sed -e "s/://g"
Utilities
Time Tamer: