Going to get a 250-480 GB SSD at some point to replace the 1TB spinner in my 2015 iMac. Now I currently have a USB 3.0 compatible dual drive docking station and also a single drive inatek USB 3.0 enclosure. If I were to mount a new SSD in the enclosure and plug it in via USB cable, I would imagine my speeds would be much better than the internal spinner. I ran a test on my current drive and I'm getting a normal 98-102 MB/s read and write speeds. Would an external SSD connected via USB 3 offer me close to the same speeds vs an internal mounted one? They don't seem to make a single drive thunderbolt enclosure, so I guess that's out of the question. Bottom line is I'm looking to run my machine and boot into macOS from the external SSD only and then use the 1 TB internal as extra storage. Anyone else doing this and how much slower would it be vs internally mounted. Is this a viable option vs mounting the boot disk internally? Because of the difficulty in having to separate the screen, I would prefer NOT to take apart my brand new 2015 iMac to replace the internal drive if I don't have to since I'm still under warranty. Extra points for being able to boot from external SSD but have the external continuously being mirrored to the internal drive in case I needed to unplug the external and boot from the internal spinner as well and have all my stuff in tact.