In the world of digital media, where storage read and write rates directly affect the time required to locate and open a source file, and then later render to drive, we want the fastest drive available to us, and the best interconnect from the computer to that storage medium.

There is quite a bit of marketing fluff in the industry around data storage devices. The most common misconception is the difference between the designed capacity of the channel and that of the attached device, given overhead, latency, and distance traveled which results in data loss and subsequent slower rates.

SATA I (rev 1.0) – 1.5 Gbit/s – 150 MB/s or 1,200 Mb/s real-world function
SATA II (rev 2.0) – 3 Gbit/s – 300 MB/s or 2,400 Mb/s real-world function
SATA III (rev 3.0) – 6 Gbit/s – 600 MB/s or 5,000 Mb/s real-world function

USB 1.1 – 12 Mbit/s
USB 2.0 – 480 Mbit/s
USB 3.0 – 5 Gbit/s
Thunderbolt – 10 Gbit/s

On a 2013 MacBook Pro, using OSX, I moved approximately 5GB data by both copy (drag-n-drop) and rsync (executed from the terminal), from an internal SATA III Hybrid drive to an external USB 3.0 drive with the following results:

  1. rsync reported 50MB/s transfer or 480Mbit/s which is exactly USB 2.0 speeds.
  2. copy (desktop drag-n-drop) – 1GB every 15-18 seconds (using a lap counter) where …

    1GB * 8 = 8Gbit / 15 = 533,333,333 or about 500Mbit/s; and
    1GB * 8 = 8Gbit / 18 = 444,444,444 or about 444Mbit/s

What I have read about rsync versus cp (copy) is true — they are identical when making fresh copies. If, however, you are using rsync to conduct a comparative update, where data between the source and target is compared for modification dates, copied and / or deleted, then this process will of course require more time.

As for the total data throughput, however, the ABOUT THIS MAC profile states my USB 3.0 devices are enabled to transfer up to 5GB/s, but clearly, they are running at EXACTLY USB 2.0 speeds which means USB 2.0 is the limiting factor, not the drives. I have read reports (as of July 2012) that while Apple claims to support USB 3.0, they have not enabled the driver to force people to upgrade to Thunderbolt adapters.

More testing is needed with my current laptop, between the internal SATA III SSD and an external SSD.

Stay tuned …