The following is obviously dumb-dumb server setup 101, but I'd say a majority of my client's have not completed this step on a majority of their servers. Approximately 10% of the servers I see have actually set this, everyone else just leaves it at default:
When you say lots of variations in performance metrics I can't help but think of an article I read when researching the validity of insuring that the default "Balanced" Power Plan is changed to "High Performance" in your SQL Server's Power Options (obviously you would do this on every Windows server because, duhh, of course we want our production servers running at their best all of the time, but he makes the point that it is extra important on SQL Servers because with a Balanced Plan the SQL Server must ask the OS for more resources, wait for the OS to approve this request, then up the resources to the next step that should satisfy SQL's needs. By that time, SQL may need even more resources than it originally requested due to more load and must ask the OS yet again for more resources. Rinse and repeat the above cycle. He claims that with a an increasing load on SQL that the OS is always a step or two behind in granting the resources it needs causing it to be slow-fast-slow-fast-slow-fast. He then proved this theory by submitting all kinds of tests and stuff (I know, super technical jargon here).
Just tried searching and couldn't find the link but I'll add it later. So, my point is, and I'm sure you all have done it, but check and make sure that your power options are set to High Performance because SQL don't like asking for it's power! :-)
