Slow VM's on Hyper-V and Windows 11

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tchart

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#295278 18-Mar-2022 12:23

Hi Folks,

I have a lab environment on a PC that was running Windows 10 Pro and Hyper-V. I have several Hyper-V VM's (around 5) that need to be running at the same time and this worked nicely on Windows 10 - ie VM's were performant.

I upgraded the host PC upgraded to Windows 11 a few weeks back and all of a sudden the VM's are very "laggy".

The host OS is fine memory/CPU wise but since the upgrade the disk activity (on the host) is often pegged at 100% even though the VM's are idle. The disk is SSD and wasnt an bottleneck on Windows 10. Even with 1 VM running (idle) the disk R/W often jumps up to 100% but the transfer rate is in the kbs.

Anybody seen anything like this on Windows 11?

I saw a few posts on Reddit of people experiencing the same with VMware but the fix was to disable HYper-V which obviously isnt a fix for me.

Also tried to install KB5007262 which apparently fixes some know SSD issue but the patch said it wasnt applicable to my system :(

Any thoughts?

Thanks

gzt

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#2888188 18-Mar-2022 12:50

Curious to know what your processor is.

gzt

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#2888192 18-Mar-2022 12:56

Last time I used hyperv desktop on windows 10 the default setting for all vm was automatic memory allocation no max. It was terrible for any multi-use scenario. Setting a defined max allocation for each machine within available ram was 100% required.

tchart

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#2888208 18-Mar-2022 13:19

gzt: Curious to know what your processor is.

The device is NUC style Asus PN50, AMD Rzyen 7 4700U with 64GB DDR4 (3200mhz).

There is no contention on the CPU. Memory allocation for the VM's is fixed.

As mentioned this wasnt a problem under Windows 10. Its only since the upgrade to Windows 11.

tchart

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#2888335 18-Mar-2022 15:19

Interestingly moving the virtual disks to the C drive fixes the issue.

While C & D are both SSD, C is NVME and D is SATA. So it could just be masking the problem since its about 4x faster.

Going to restore windows 10 and see if the problem persists.

tchart

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#2890678 23-Mar-2022 14:06

So reverting to Windows 10 did resolve the issue, the VM's are nice and snappy now (eg no lag when logging in via RDP, start menu opens immediately).

What is interesting is that the disk is as busy as it was on Win 11 but the VM's remain snappy on Windows 10. I ran Crystal Disk Mark on Win 11 before I reverted and on Win 10 afterwards. There was no difference in stats so it doesnt look like a disk access issue.

Anyway, Im happy that my VM's are performing again.

TLDR; stay away from Hyper-V on Windows 11

TwoSeven

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#2890842 23-Mar-2022 16:23

Just my thoughts, but from memory, when a machine is waiting for I/O the CPU may likely show 100% as it will be waiting for said I/O to occur and present it with some data. If the CPU on the host isn’t showing activity but ones disk controller is, then the issue may likely be that one has ones VHDs on a slow disk.

SATA I think uses AHCI and likely will be likely have an upper limit at around 550MB/s, I think perhaps a NVME drive will likely do double that on a single PCIe 3.0 lane - and it still has another 4 lanes that it can use.

Some tests might be allocating more memory to the VM to reduce swapping and setting a fixed amount of memory as mentioned above.

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