When my moodle server is crawling...

What is happening? 

Why is my server so slow?
Is some process eating up my CPU cycles?
Is there too much in memory?
Did I leave a setting like Theme designer mode active? 
Is there something causing moodle to not cache? 
Do I need more indexes in my DB? 
Did a recent upgrade of my moodle create a rogue process? 
Is a cron script running? 
Are there fifty simultaneous requests being executed?
How long has it been slow like this?

I need a tool to measure the servers performance.

In hind site, that's a few days later, the reason the site was crawling is because drive space was getting low, low, low.