A newly installed Win 10 Pro in Hyper-V (4GB Ram, 32GB HDD) with all latest updates and NOT a single software had been installed yet! Except these two tools:

1. Classic Shell
2. 7zip

Both of them were downloaded from official site.

After installing, the windows were cleaned using cleanmgr to release all the HDD space.

And that stupid windows defender had been running and scanning since yesterday night. Non stop.

Luckily it was not installed on my SSD, otherwise it will generate > 1TB of write in less than 3 hours. (I used to have this problem on the host, and that is the reason why I have disabled windows defender)


WTH is Windows Defender doing? If it is scanning, it shouldn't write too extensively to the HDD.

Furthermore there is NOTHING To scan. I have only a 32GB HDD, and with less than 10GB of files installed (including the OS)

This post has been edited by CKKwan: Jun 15 2017, 08:15 AM


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Too many reported cases over years and still buggy. It is useless in my opinion

im using it without issues, not sure bout ur case.

Because you are not monitoring its performance.

well don't blame purely on windows defender. What I noticed on a newly installed windows whichever version if you install all updates especially those .net ones after that the performance are affected for a while.

You may want to disable defender if you already have a reputable anti virus program.

1. Open regedit: Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SecurityHealthService

2. Set the start type to 3.

3. Go to Task Manager, Startup, right click on Windows Defender Notification icon, click Disable. Reboot. Problem solved.

Actual disable step here.


You may also read the story where Microsoft got bash! here.

how sure are you it's windows defender? From your screenshots can only see hdd thrashing. It could be pagefile swap due to insufficient memory or file indexing running or cortana indexing.

If you goto the Process tab, it will shows "Antimalware Service Executable" is the one that hogging the HDD.

Besides, all the CPU and HDD activities drop to near zero (0) once I have disabled Windows Defender using gpedit.

the allocated virtual ram is not 4gb. from screenshot it's 2. running w10 with 2gb ram might trigger swap use more often, causing 100% cpu usage also.

i run w10pro on virtualbox. (4gb ram; 40gb hdd) i only have brief moments of high ram usage sometimes, not always.

The Allocated RAM is 4GB. Hyper-V will dynamically increase / decrease the RAM available.

Besides, there isn't any software running at the moment. Only Windows Defender was running at the background.

i only use window defender for antivirus
it's quite useful for my laptop

dynamically allocated ram is a nice feature in hyper-v in theory, but sometimes it doesn't work as expected. in general, a w10 vm with static 2gb runs better than a vm with 4gb dynamic ram in hyper-v. (just try it out if you want)

however, i agree that windows defender is the most common app that causes full disk usage (especially if the os/vm is on hdd). for relatively optimal use, run vm on ssd, and do some manual tweaks to it.

This post has been edited by horns: Jun 16 2017, 03:49 PM

But in this case, I do not think that the high HDD usage is caused by the dynamically allocated RAM.

maybe; but it contributes to overall sluggishness due to much lower iops. looking at that high cpu usage, i suspect swap file on hdd was in action.

Besides dynamically allocation of Memory, Hyper-V also dynamically scale back the CPU time allocated to the VM. That is why a lot of time you will notice CPU usage is very high.

Windows Defender shouldn't use so much memory that it causes the OS to start swapping into HDD. When memory is not sufficient, Hyper-V should first allocate more from the host (until its limit is hit) before telling the OS that there is no sufficient memory and triggered a swap. Besides, Windows Defender is (the only) actively running, if the OS wish to swap some thing out of memory, it should have swap something (which is idle) else instead of Windows Defender.

er what you said are ok, in general, on paper. problems lie in behaviors of hyper-v during actual applications. maybe dig a little deeper on common issues and best practices of hyper-v.

i understand that your main point is about how bad windows defender is. however i run w10pro vms for some times now (virtualbox and hyper-v; fixed 4gb ram; 4 cpu vcores). windows defender doesn't give me high cpu/disk/mem issues so far.

The theory (deep inside) will basically affect all applications running inside hyper-v. Which is a MORE serious problem than just Windows Defender alone.

If whatever you said is true, then you should have noticed that your VM is behaving unexpectedly.

the thing is that i don't have such a problem

That is fine, I only disagree with your weird theory

ok and sorry for annoying you with my 'weird' theories. just ignore them all.