I own the base model 15" MacBook Pro (Mid-2015) with the 256 GB SSD. I have been living with lots of external hard drives for some time now, but I would like to move my iTunes library to my local machine. I already save lots of space on my local machine, by simply using Google services for just about everything -- all of my photos and backups are on Google servers. The only thing that takes up space now is my iTunes library and general scratch data. I would like roughly divided as follows: 50 GB scratch, 50 GB system, 150 GB iTunes, with 128-256GB for "extra" iTunes data -- films, tv, etc. I suppose that I am left with two options: an aftermarket PCIe SSD upgrade, or a very large SD card. On the aftermarket SSD -- are there actually many options here? What is the typical price range and are they as good as the Apple supplied ones? On the SD card -- how reliable are they for long term storage? £36 for 128GB is a cracking deal. I would appreciate your thoughts.