My host OS is Windows 10 with anniversary update.
My guest OS is also Windows 10 with anniversary update.
I was facing this issue while running virtual machines on VMWare Workstation 12. I guess I had this issue for long but I felt a need to really look into this after Windows 10 anniversary update. My virtual machines were really slow.
Even at this moment I am not sure whether it had anything to do with anniversary update and/or windows 10. However, my task manager activities showed me that Windows Defender was locking some files where I had my virtual hard drives created. The solution was to exclude all the folders where the virtual hard drives were stored. I had stored my virtual hard drives locally on my host machine on a separate SSD drive.
For a good measure I also excluded VMware folder available in C drive to make sure that Windows Defender let VMware executable and other components run without blocking.
I am not sure why Windows Defender looked at them skeptically but it was clear that there were being constantly looked by Windows Defender. I guess .VHD files are being updated very frequently by VMWare Workstation when an associated VM is in use. Windows Defender might be tracking them constantly as they were being updated very frequently. That should result into files being locked and unlocked. This might prevent VMWare to work efficiently.
Well... whatever be the reason; I was able to run my VMs efficient after the above change. Now I can run simultaneously 6 instances of Visual Studios, one instance of SQL Management Studio, an Outlook client, a few instances of Edge, a TypeScript compiler and a Node engine with only 4 GB of ram and 2 processors. I had put in 10 GB of RAM and 8 processors earlier and was still running into the issues. Now it looks like that I could utilize the full power of Windows 10 and a 64 bit machine.
I hope that this solution might help to someone who is facing the similar issues related with Windows Defender.
Thanks a lot for visiting my blog. Wishing you a happy virtualization!