While we were waiting for the "Retina" MacBook Pro to arrive, we kept ourselves busy testing various USB 3.0 drive enclosures connected to the USB 3.0 ports of the 'mid 2012' MacBook Air. Then, for perspective, we threw in results for USB 2.0, FireWire 800, eSATA, and Thunderbolt enclosures. Our goal was to put USB 3.0's real-world transfer speed in context with other interfaces.
GRAPH LEGEND
MBA Internal = 6Gb/s SSD inside the 'mid 2012' MacBook Air
CalDigit Tbolt = CalDigit T1 Thunderbolt enclosure with Intel 480G 6Gb/s SSD
Echo T-SATA* = Sonnet Echo Pro Thunderbolt-to-ExpressCard-to-eSATA adapter with 6Gb/s SSD
GoFlex Tbolt = Seagate GoFlex Thunderbolt Adapter with OWC Electra 6Gb/s SSD
Elgato Tbolt = Elgato Thunderbolt SSD (with SanDisk Ultra 3Gb/s SSD)
LaHub T-SATA* = LaCie Thunderbolt-to-eSATA Hub with 6Gb/s SSD
Koutech USB3 = Koutech ASU330 USB3 bridgeboard with 6Gb/s SSD
Promini USB3 = OWC Mercury Elite Pro mini eSATA/USB3 enclosure with 6Gb/s SSD
Enyo Flash USB3 = OCZ Enyo 128GB USB 3.0 Flash Drive
On-The-Go USB3 = OWC Mercury On-The-Go USB 3.0 enclosure with MBA 3Gb/s flash storage module
Voyager HDD USB3 = NewerTech Voyager USB 3.0 Dock with Hitachi 7K3000 HDD
Lexar Flash USB3 = Lexar JumpDrive Triton USB 3.0 32GB Flash Drive
TT Duo FW800 = CRU-Dataport ToughTech Duo RAID 1 enclosure with 6Gb/s SSDs to FireWire 800 port
Enyo Flash USB2 = OCZ Enyo USB 3.0 Flash Drive connected to USB 2.0 port
(*The term "T-SATA" is one we coined to describe a Thunderbolt-to-eSATA adapter.)
Unless otherwise noted, all "6Gb/s SSDs" were OWC Mercury Extreme Pro 6G SSD.
INSIGHTS and ANALYSIS
I know there's a lot to consume in the above graphs. To summarize, USB 3.0 is dramatically faster than USB 2.0 and FireWire 800, but not as fast as T-SATA, SATA, and Thunderbolt storage solutions.
There's a lot of USB 3.0 enclosures to choose from but our graph shows that, in terms of performance, they are not all created equal.
And none of them came close to the theoretical speed of USB 3.0. The "SuperSpeed" bus provides a transfer mode at 5.0 Gbit/s additionally to the three existing transfer modes. The raw throughput is 4 Gbit/s, and the specification considers it reasonable to achieve 3.2 Gbit/s (0.4 GB/s or 400 MB/s) or more. The fastest USB 3.0 transfer speed we've recorded is 275MB/s using the HPT RocketU Quad USB 3.0 host adapter on a 2010 Mac Pro connected to the Koutech ASU330 bridge.
One adapter we didn't include in this round was the NewerTech USB 3.0 to eSATA adapter. You use it to connect an eSATA enclosure to a USB 3.0 port. It is capable of 200+ MB/s and it only costs $25.
BOTTOMLINE: The addition of USB 3.0 to the 2012 Apple laptops is welcome (and long overdue).
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