Performance counter for Hyper-v host StorageIOPSUsage value.

I am looking into the performance counter StorageIOPSUsage of VMM for Hyper-v host. Just wondering how SCVMM collect this counter value and what counter type it use to calculate StorageIOPSUsage value.

I believe SCVMM use Physical Disk counter to get the StorageIOPSUsage if it is true then  what all value does it use to calculate StorageIOPSUsage. Is it the sum of Avg.Disk Bytes/Read and Avg.Disk Bytes/Write (25,258.667+4,992.000=30250.667) or sum of Disk Read Bytes/Sec and Disk Bytes/Sec (151,353.416+19,941.835=171295.251)