USB/Ethernet unstable on Beagleboard xM Rev.C Ubuntu 11.10 and 12.04

I have recently purchased a beagleboard xM and want to make it a low power server.

Currently, I connect a usb hard driver to the board. Had samba server configured and working. When I put the system into real work. I found the usb or ethernet go dead after 10-30 min large file transferring. The date transfer rate is about 5 MB/s continuous for about 20 min, then the LED on the ethernet port will be turned off. I also cannot get the ethernet card information from ifconfig. Only the lo network is shown after that. Resting the board can solve the problem. But it can come back buy simply copy another big file to the samba storage. In the other way, downloading a big file from samba server can also cause the problem. I kinda believe it is the usb problem. Since after the ethernet stoping working, I cannot read anything from the usb hard driver either.

My beagleboard has both Ubuntu 11.10 and 12.04 installed on separate micro SD card. The bug happens on both armel and armhf architecture.

Is it a software bug in the ubuntu kernel or a hardware fault? Anyone has the same problem?

Just curious: do you experience any performance issues with kworker?