Think through your requirements and data throttle points before investing in a bus-powered Thunderbolt drive. - by David R. Beebe
Talk about not thinking a plan through, I was excited to take advantage of the theoretical data transfer speeds offered by the new Thunderbolt interface available on my MacBook Air. The Buffalo Mini-station bus-powered 500GB Thunderbolt/USB3.0 portable drive seemed like a great addition for speeding the transfer of RAW photos and AVCHD video in the field. What I failed to realize was that the source material was still constrained to USB 2.0 speeds.

In a side-by-side compare, I timed the copy of a nearly full 32GB SDHC Class 10 card via IOGEAR 56-in-1 Memory Card Reader/Writer. I first copied the data to a Seagate FreeAgent Go 500GB bus-powered USB2.0 drive. I then repeated the copy to the Buffalo Mini-Station drive over Thunderbolt. Because the Thunderbolt I/O was slowed by the data transfer rate from the Card Reader, the transfer time only went from 31 minutes to 28 minutes. Certainly not the transfer times one would see if the source was faster.

A Thunderbolt Card Reader is still throttled by the transfer speed of the memory card. It would have to also be a pass-thru device since the Buffalo Mini-station drive has a single Thunderbolt connection. The Sonnet SxS Memory Card Reader With Thunderbolt with a separate ExpressCard/34 CF reader or ExpressCard/34 SDXC reader also has 1 Thunderbolt connection. This solution cannot deliver Thunderbolt speeds as it is limited to ExpressCard speeds. This means copying the data to the MacBook Air's SSD first. No matter how fast this is, there is little reason to do 2 transfers as a time saver.

That minimal 3 minute (10%) savings in transfer time comes with its own costs. First, the Thunderbolt drive is easily 2x more expensive that comparable USB2.0 portable storage. Second, the bus-powered Buffalo Mini-station runs hot. Much like a bus-powered FW800 drive, you could use this as a hot plate. All that heat comes from extra power drawn from the MacBook Air's battery. Running the Thunderbolt drive, a full charge on the Air's battery is consumed very rapidly (around 1 hour). Third, the drive is nearly double the weight of a USB2.0 drive.

This is not to say that Thunderbolt cannot live up to its promise for speed. A new Time Machine backup from the MacBook Air's 128GB SSD was very fast. Still, had I thought this through, I would probably have waited longer before buying this technology.