Andy Galbraith is starting a new toolbox series. His first post is an introduction and a look at drive latency:
You look at the numbers again, and now you find that disk latency, which had previously been fine, is now completely in the tank during the business day, showing that I/O delays are through the roof.What happened?This demonstrates the concept of shifting bottleneck – while CPU use was through the roof, the engine so bogged down that it couldn’t generate that much I/O, but once the CPU issue was resolved queries started moving through more quickly until the next choke point was met at the I/O limit. Odds are once you resolve the I/O situation, you would find a new bottleneck.How do you ever defeat a bad guy that constantly moves around and frequently changes form?
Click through for some pointers on disk latency and trying to figure out when it becomes a problem.