What is the impact of sharing the Virtual HD storage device with the Windows OS on a virtual machine?

If you are running a virtual machine with 2 Virtual HD storage devices, one is shared with Windows OS and the other is for applications, you can run two sets of SQLIO tests to see the impact of the Windows OS running on the storage device.

Here is a comparison of the 64-KB reading benchmark on Virtual HD "C:" which is shared with Windows OS, and "D:" which is for application only.

C:\fyicenter\SQLIO>sqlio -LS -kR -b64 -i64 -f64 -t1 -s30 -p0 D:\testfile.dat
MBs/sec:   348.80

C:\fyicenter\SQLIO>sqlio -LS -kR -b64 -i64 -f64 -t1 -s30 -p0 C:\testfile.dat
MBs/sec:   232.13

Here is a comparison of the 64-KB reading benchmark on Virtual HD "C:" which is shared with Windows OS, and "D:" which is for application only.

C:\fyicenter\SQLIO>sqlio -LS -kW -b64 -i64 -f64 -t1 -s30 -p0 D:\testfile.dat
MBs/sec:   344.54

C:\fyicenter\SQLIO>sqlio -LS -kW -b64 -i64 -f64 -t1 -s30 -p0 C:\testfile.dat
MBs/sec:    12.43

As you can see, sharing the storage device with the Windows OS has some significant impact on I/O performance. In case of reading, sharing with OS lows the speed from 348.00 MBs/sec to 232.13 MBs/sec. In case of writing, the impact is even bigger, from 344.54 MBs/sec to 12.43 MBs/sec.

⇒ Azure Virtual HD on Windows 10 - SQLIO Tests

⇐ Virtual HD ATA Device on Server 2016 - 1-MB Benchmark

⇑ I/O Tests on Azure Virtual HD and Storage

⇑⇑ SQLIO Disk I/O Benchmark Test Tutorials