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VM running Windows Server 2019 is very slow


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Hello everyone!

I have a VM running Windows Server 2019, and it started to run extremely slow. First, I thought that the cause could be some memory issues. So I checked it. It turned out I have almost 2 GB of RAM for the host VM. Isn't it enough? If so, what else should I check? Because I'm really tired of this slow performance.

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Hi, @heyho!

One of the most typical reasons for poor VM performance is insufficient hardware resources. It would be best if you avoided the memory and CPU overcommitment. What should you have in the account?

1. CPU resources. Suppose your VM lags: consider using more CPU cores or adding virtual processors. In case your processor is old, think of upgrading the hardware of a host machine.

2. RAM for the VM. Ensure setting a sufficient amount of RAM for your VM. If there isn't enough memory, the guest OS will have to actively rely on swap files, leading to slow performance. However, assigning too much memory to a VM isn't the best idea because you should leave some RAM for the host.

3. RAM for the host machine. Assigning excessive memory to a VM usually means a lack of RAM for the host OS. In this case, the host OS will use swap files intensively, which leads to the degradation of the performance. 

How to find the right amount of memory?

For this, you should check system requirements for the OS and applications. However, you can rely on the perfect ratio. For instance, your host machine has 8 GB of memory while running Windows 10 or ESXi 7.0 with VMware Workstation (Windows Server 2019 VM). If you set 4 GB of RAM for a VM, 4 GB is left for your host OS. It is more than enough for decent functioning. Note: This example doesn't include additional applications that might consume significant resources. 

In this case, the ratio is 1:2 (meaning 4 GB to 8 GB). What we get is 1/2-1= -0.5. -0.5 is the current MEM overcommit average value. 

Remember to keep the balance, because if you provide 2 GB of RAM for the same VM, VM performance will be poor. On the other hand, if you set 6 GB of RAM for the VM, the host machine won't get enough memory. As a result, both physical and virtual machines will degrade. 

You also have to take into account the heavy applications you run on VMs (e.g., databases). You might adjust VM configuration and add additional memory and CPU resources.

If you require more information on performance problems, check our blog post https://www.nakivo.com/blog/a-full-overview-of-vmware-virtual-machine-performance-problems/  and don't hesitate to contact me, in case you have any questions. 

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