I have a machine that I'm trying to troubleshoot -- could be a hardware problem, could potentially be a software problem. It's a Dell PowerEdge 2950 (with a couple of dual-core 3.5GHz Xeons) and I've just installed CentOS 6.2 on it.
If I do 'dd if=/dev/zero of=/dev/null', I get transfer rates of around 30 MB/s. On other similar machines, I'm getting 500 MB/s or even 1.2 GB/s. So something is clearly amiss -- as far as I can tell, something must be sucking up the machine's CPU power (that dd doesn't do any I/O), but neither mpstat nor sar shows me anything obvious. Nor are there any messages in /var/log/messages or /var/log/dmesg that tell me about re-presenting interrupts or the like.
So I'm somewhat out of ideas -- the machine is clearly sick but I can't figure out how. I'd love any bright ideas for things to try!