Hey... I am about to order my new iMac and coming from the PC world I am not sure which storage to select. My initial thought was to go for 256 SSD and then (eventually) go out and buy a 512 or 1TB external SSD. I have no idea how much space MACOS will take up, but I am guessing it's not more than 50GB, which would leave me with 200GB of space for my documents. The External SSD would still be pretty fast I guess and I would use that for video, music and other stuff like that. This question may sound a bit silly, but I have absolutely no idea how the file-system works on a MAC and how to structure files (could I have all my documents on the EXT for example). Anyway, what I am basically asking, is if there is good reason to spend the extra money on internal storage vs. getting more external for the same money
OS X takes up less than 20GB in a fresh install configuration. You can spend on a 256GB internal PCIe SSD and buy an external SATA3 SSD that works over Thunderbolt and it'll be plenty fast. Thunderbolt is highly recommended because TRIM works over TB and not USB. As long as the external drive is formatted as Mac OS Extended (Journaled) for OS X use only, or ExFAT or FAT32 for cross platform usage, you're good to go.
Okay, so I need to get a drive that supports thunderbolt? Is it only apple-drives or do other manufacturers make TB drives as well? (sorry, brand new world for me)
It's really not that simple. They might have 2x the maximum large block transfer rate, but they don't have half the access time nor 2x the transfer rate for small files. In short, the internal PCIe SSD is not twice as fast at anything other than transferring large files. For booting, launching programs and general usage, you'll barely notice any difference between an internal SSD and external. It's a bit like saying a Ferrari is twice as fast as a Mini. Not around town it isn't ;-)