We have found that USB flash drives build profiles at a variety of speeds. In some cases, we have found building a Basic Profile can take in excess of 4 hours. In our testing, the best case for building a Basic profile on a USB 2 drive is a little less than 2 hours using SanDisk drives. Hard drives are typically much faster, usually taking less than an hour.

We're still benchmarking USB 3 flash drives, and should post recommendations here in the future.