So my 2011 Mac Mini bit the dust the other day and I ordered the 2017 iMac with a 256 GB SSD. The Mac Mini had about 460 of the 500 GB used up and I have that backed up on my external drive. I will be setting up my iMac as new and will be transferring the files that I want to the computer and accessing the rest from the external drive. My question is this: how can I use my backup drive as both an external drive for my computer and as my Time Machine backup? Is it as simple as partitioning the external drive?