Hyper-V Dynamic memory doesn't go back down

Abraham 1 Reputation point
2021-04-27T21:51:01.787+00:00

We have Hyper-V running on 2012 R2, I noticed that whenever the VMs memory usage spikes for whatever reason, they HV will assign more RAM to them, but when the VM's are idle, the HV doesn't reclaim the RAM that was assigned, thus, causing constant resource shortages.
Total RAM is 32 GB, 4 VMs total, 3 of them have a minimum of 2 GB and 8 GB max, the 4th has a minimum of 2GB and 20GB max.

VMs 1-3 are DC, File Server and App server but they rarely go over 4GB, still, when they're idle, allocated RAM remains at 4GB
VM 4 is a backup server, each backup job takes up to 2GB so it can easily reach the 20GB limit, this server works mainly at night, with only 2 backups running during the day, so technically there shouldn't be a resource issue

But since RAM is not dropping once the backups are done, we are constantly finding paused/locked VMs in the morning.
I couldn't find a similar issue posted before so I decided to ask and see if anyone else has gone through this.

Hyper-V
Hyper-V
A Windows technology providing a hypervisor-based virtualization solution enabling customers to consolidate workloads onto a single server.
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  1. JiayaoZhu 3,911 Reputation points
    2021-04-28T06:14:48.02+00:00

    Hi,

    Thank you for your posting!

    Based on your descriptions, firstly, there are many reasons that can cause to your issue, such as dynamic memory configuration and 2012 R2 version limitations and I would like you to firstly self-check your issue following the guidance and self-solve your issue in these articles:

    https://www.altaro.com/hyper-v/best-practices-for-hyper-v-dynamic-memory/

    (Please note: Information posted in the given link is hosted by a third party. Microsoft does not guarantee the accuracy and effectiveness of information.)

    https://support.microsoft.com/en-us/topic/vms-may-not-get-additional-memory-although-they-re-set-to-use-dynamic-memory-in-windows-server-2012-r2-5724bb44-197f-91ec-2ad2-fba5b538ccab

    Secondly, regarding the memory configuration, I think you can check this article to better understand your suitable settings:

    https://itproguru.com/expert/2013/01/inside-dynamic-memory-in-windows-server-2012-hyper-veverything-you-need-to-know/

    (Please note: Information posted in the given link is hosted by a third party. Microsoft does not guarantee the accuracy and effectiveness of information.)

    I also found a blog whose issue is similar with yours:
    https://learn.microsoft.com/en-us/answers/questions/67848/hyper-v-dynamic-memory-not-working-windows-10.html

    Thank you for your support!

    BR,
    Joan

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