Friday, February 22, 2008

USB Flash Drive Characteristics

We recently had two papers accepted at the upcoming IEEE WoWMoM, one on loss sourcing in 802.11 (more info in a later post) and the other on USB flash drive performance characteristics with respect to read/write speeds and power consumption. The work itself was done in large part by one of my summer REU students which is very cool to see those results turn into a tangible research output.

The paper in itself was an outgrowth of discussions related to a DARPA WAND proposal from last year. While we weren't funded, we had proposed the usage of USB flash to provide a cheap and easy method for significant on-demand storage for our packet caching architecture. There were some discussions that the flash drives would be too expensive power-wise and we were at a loss to directly respond to that. Long story short, that led to the above REU project to pin down the energy costs and performance of the drives which would be a necessity if the grant got funded (it was not, unfortunately).

The net result was that our initial hypothesis was correct, i.e. the cost of the flash drive in terms of power was dwarfed by the cost of the wireless adapter itself, especially in a USB 1.1 setup that would have likely been in place. We were not entirely vindicated as we discovered that by in large, the flash drive itself would never enter a low power mode when not in use, i.e. the file system is in essence permanently mounted which in turn triggered periodic "Keep Alive" messages across the USB bus, never allowing the flash drive to enter suspend mode. The REU student did a nice job diving into the ugly innards of the Linux kernel USB module to hacking up a suspend API for some basic testing. While it did offer the option to manually force a suspend, the performance results that could certainly use some tweaking as it would be ill-suited for significant amounts of suspend/resume operations.

All in all, a neat project for a REU. We posted a Wiki form version of the original submission here if anyone would care to peruse it. The final camera version of the paper (accepted as a short paper) will be posted in the next month or so to the website and will be available on the same link. The USB flash profiling tool is also posted on-line available via the same link or the above direct link.

Finally, I am finally taking the plunge and starting a policy of putting reviews from accepted papers on-line when I can. The nice part is that it gives us a chance to do a minor rebuttal but also it gives some nice transparency to the review process which in my opinion is a very good thing. The review / response notes for the paper can be found here.

Tuesday, February 19, 2008

New Cisco Research Site

For those interested, Cisco has a new front-end for Cisco research.