Do you have any sort of trending or monitoring running against this box? If not, it may be very difficult to diagnose. This behavior could be caused by any number of things. Here are a few ideas off the top of my head:
- transient network glitch (broadcast storm, routing loop, spanning tree topology change, etc)
- IO Contention (did something consume all the RAM of the server, causing it to go heavily into swap land?)
- did the server reboot?
Going forward, I'd highly recommend getting something like Munin set up. With Munin, you'll be able to easily keep tabs on disk IO, memory usage, CPU usage, process count, network traffic, etc. Having this information makes it much easier to troubleshoot this sort of problem. Alternatively, you can install and set up
sar, which gathers much of the same data, but logs it in text files, which you can inspect after the fact.