is it worth it to install SSD internally, instead of using USB3? I prefer to keep my boot drive external, so that I can quickly boot using another Mac if my primary Mac fails. I use a USB3 drive dock to connect the drive to my Macs.

I bought a 120GB SSD w/SATA3 (6.0Gbps) interface, capable of pushing >500MB/sec read and 260MB/sec writes, sustained.

USB 3.0 is pretty fast -- spec'ed at 5.0Gbps. I'm thinking that performance over USB 3.0 should be at least in the same ballpark as SATA3 (6.0Gbps). It's about an hour of risky, careful work to install the SSD internally in my Mac Mini, is it worth it?
YES, it's definitely worth it. With my setup, sustained transfer speeds were roughly 75% better using SATA, vs. USB3.



I tested both configurations using ZoneBench as follows:

SSD: 120GB OWC Mercury Electra 6G 

Mac: Late 2012 Mac Mini, 2.6Ghz core i7, model ID Macmini6,2, 16GB RAM

Hot-Swap unit: StarTech USB3-to-SATA dock, model SATDOCK22U3S ver2

  All speeds are in MB/sec (mega-bytes per second)

  Configuration A: SSD connected via Hot-swap USB 3 Dock
  Lowest / Avg / Highest R/W speeds:  95 / 150 / 185

  Configuration B: SSD installed in internal HDD bay in 2012 Mini (direct SATA):
  Lowest / Avg / Highest R/W speeds: 145 / 250/ 460


All tests were repeated 5 times at intervals of 1 hour, under normal system usage. (A few apps open &amp; idle, CPU &amp; system I/O load 99% idle.)



As one can see, in this configuration, taking the trouble to mount the SDD in the Mini's internal SATA bay is well worth the massive performance gains.