I use one of my Raspberry Pi's as a NAS, storing backup copies of some files on two USB hard discs. Today I tried syncing one of the directories that I back up to the Pi, and noticed the speed of transfer across the network has dropped. I used to get around 100Mbps, but now the speed has dropped to about 30Mbps. It does sometimes start at the higher speed, but then drops back. Does anyone have any ideas? The only thing I can think of that has changed recently is the new kernel and firmware that were released along with the new version of Rasbian. I did also lightly vacuum the Pi and its surroundings today, so it is possible I knocked something. I did shut down the Pi, then disconnected and reconnected all of the connections and tried again, and the Pi is still showing the same slowdown, so it's probably not that. Any suggestions would be welcome. As a first step, to rule out the new kernel and firmware, can someone tell me how to roll them back to the previous version?