....I'm guessing your machine only allows one internal hard drive. So, the absolute best SSD tp use is the brand new Samsung 1 TB 850 Pro internally......this drive is expensive,but, is the absolute best...esp. for video.It just about saturates the SATA III interface with read AND write speeds of around 550MB/sec. If you have a Thunderbolt port, you may attach another such drive within a Thunderbolt enclosure and hopefully will get similar speed....without needing a RAID box of any kind....( which is another option to consider, esp. if you need to have a large capacity....you would use one on the Thunderbolt port). The OLD recommendation was to always have at LEAST two separate drives MINIMUM, of at least 7200rpm. NOW, the SSDs are SO FAST, you can work with just one, if absolutely necessary...but BEST to have TWO or more.With my laptop that has 2 internal drives I can place all the previews,media cache, and media database on a third external drive.....PPro simply recreates THOSE files, if that 3rd drive was not available.
I agree with JFP...above. But if you have a USB3 interface on that MacBook, you can also try using it as I have on my PC laptop
For simplicity on my PC laptop I would just go with a fast USB3 flash drive for the project and media files. I have several PNY Turbo USB3 128GB units and have recently edited a 1-hour long three AVCHD camera shoot (not multicam mode) with perfect ease. That way you do not have power cables from hard drives. I suspect that the new SanDisk Extreme Pro will match those speeds below but at a much higher cost ($140 versus $50). Never believe the manufacturers speed claims here are real achievable results on the PNY.
That read speed is better than most hard disk drives as it does not fall off as the storage device gets full, and the access time is significantly better despite significant USB overhead.