Hyper-V Disk Speed Musings

Hyper-V Disk Speed Musings

I was testing out the Intel 905P and getting the benchmark numbers, I also went ahead and installed HyperV, set it up correctly, and then created a Windows 2016 VM running and decided to run the same CrystalDiskMark benchmarks again, in the HyperV host as well as inside the VM.

I only had the one VM running, and the host was not doing anything other than hosting whilst I was running the benchmark

On the queue depth of 32, sequential reads and writes are where they should be.

On to queue depth 32 random reads and writes, and we can start to see a penalty.  Just wait.

At a queue depth of 1, sequential reads and writes are looking not too shabby.  The VM itself sees a reduction on reading, but not too bad.

And here we get to the interesting part.  Look at the random reads and writes from inside the VM.  I ran this test multiple times and the result was nearly the same numbers at every go.   From a VM, raw disk performance sees a tremendous, nay, massive hit.

I went so far as to reboot the host, rebuild the mirror, and ran the numbers again.  Each time was basically the same.  I made sure the virtual disk on the VM was not throttled, and it was a Gen 2 VM.

Quite odd.  I’m hoping to soon be able to test to see if perhaps the VHDX auto expanding setup was the culprit.  Stay tuned.

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