Is USB 2.0 with a 7200RPM drive enough, or should I invest in either an eSATA Expresscard adapter, or the secondary hard drive sled that my laptop allows me to use? I know either of the later would be preferred, but can I get away with USB? Thanks for any input.

Thanks for the comments. I’ve typically used a FireWire 800 based GRAID Mini to record DVCPROHD on my MacBook Pro. A single 7200 RPM USB drive will work if it’s regularly maintained. In testing, we saw that a heavily fragmented drive started triggering the “drive too slow” error message from OnLocation. Keeping the drive defragmented prevented this problem.

Let me take a moment to explain what this message means – OnLocation uses a RAM memory buffer to ensure no loss in dropped frames. The incoming video signal is first buffered in the available RAM, and it writes the data to disk after. If something hiccups on the drive for a moment, the RAM buffer fills up, and then when the drive speeds back up, the buffer is written out to disk.
If the buffer fills up past a comfortable margin (I think it’s around 35%), you’ll see this error message. No frames are lost at this point, but you should consider stopping recording soon. If the buffer continues to fill up, there’s a second-tier error that pops up, alerting you that the buffer is almost full, and you should stop recording.

As a “worst-case” test, I once tried using a 4200 RPM drive for capture of DVCPROHD footage. OnLocation complained the whole time that the drive was too slow, but as long as I recorded very short clips, the resulting files were fine. I never let the buffer fill up all the way, so eventually (when I stopped recording) the data was written to the drive. I’d never recommend this for real-world production, but understanding how the RAM buffer works helps explain what speed drives are necessary.