It is well known very small files copy ultra slow on flash memory.
As well, unlike a hard disk drive, which just writes over the old data, flash memory actually erases the data and then writes the new data. The processor requires an extra step, which results in slower performance [ref: tomshardwareguide]
I am unfamiliar with potential improvements with eSATA usb, or usb3 options for flash media.
Here's some avg data from some tests I was running today (why Iran into this thread)
500GB 7200rpm Hitachi 0.5" HDD - tiny file test
4k:1280 Average Write Speed:6.81MB/s
4k:1280 Average Read Speed:11.04MB/s
2k:2560 Average Write Speed:8.19MB/s
2k:2560 Average Read Speed:6.94MB/s
Avg Flash Drives tiny file Test (Datatraveler 32GB, 16Gb, and 8gb)
4k:1280 Average Write Speed:0.31MB/s
4k:1280 Average Read Speed:3.73MB/s
2k:2560 Average Write Speed:0.16MB/s
2k:2560 Average Read Speed:1.92MB/s
eSATA USB - could not test
USB3 - could not test
Of course, the benchmarks shared here do not take into consideration real-world type usage, where files of varying sizes typically are being transferred.
However, while there are utilities available for investigating more deeply, it seems many people already have, and my opinion in general, from my own experience, is usb2 flash stick media just cannot standup, speed-wise, to a hard drive.
-just my two-sense-