A little bit of play when measuring #SQLServer Resource Governor resource pool reads vs LogicalDisk reads

I use perfmon a lot :-)

So I'm always looking for new patterns.

Today I just happened to graph these two perfmon metrics against each other.  Perfmon was collected with a 30 second interval here.

Its not too surprising that there is a difference.  But how could there be *more* read IOs per second for the default workload group than the total on the server? (See just before 4:00 for a great example.)

Maybe if I sum the two metrics over the 4 hour period they'll even out?

23446639.19   << sum of LogicalDisk reads
22787670        << sum of default pool reads

Huh.  LogicalDisk reads are 2.89% higher than default pool reads.  Not too hard to believe - but for the small stretches where the default pool reads are significantly higher.

Oh well.

Works well for trending.  Not so well if trying to accurately count individual reads.