In this article, Kevin Holman explains how to write, and how not to write, logical and physical disk monitors in System Center Operations Manager and Essentials.
Kevin writes: This is something a LOT of people make mistakes on – so I wanted to write a post on the correct way to do this properly, using a very common target as an example.
When we write a monitor for something like “Processor\% Processor Time\_Total” and target “Windows Server Operating System”…. everything is very simple. “Windows Server Operating System” is a single instance target…. meaning there is only ONE “Operating System” instance per agent. “Processor\% Processor Time\_Total” is also a single instance counter…. using ONLY the “_Total” instance for our measurement. Therefore – your performance unit monitors for this example work just like you’d think.
However – Logical Disk is very different. On a given agent – there will often be MULTIPLE instances of “Logical Disk” per agent, such as C:, D:, E:, F:, etc… We must write our monitors to take this into account. (continue at source)