SOLVED: Can You REDUCE CPU Core Count or RAM in VMware Without Powering Down the VM

We recently worked with a client who had a mission critical server they did not want to power down to make hardware changes to. They were thinking because the server was a modern Windows Server 2019 running on VMware 7 with Memory Hot Add enabled, that they could avoid powering down the VM.

REDUCING CPU CORE COUNT:

Reducing the number of CPU cores in VMware Cloud Director on a Windows Server 2016 and newer without powering off the VM is possible but not recommended.

REDUCING RAM MEMORY ALLOCATION:

Unfortunately, reducing the amount of RAM in VMware on a Windows Server 2016, 2019, 2022, or Server 2025 VM without powering off the VM is not supported, even if the VM is configured with Memory Hot Add. The Memory Hot Add feature allows you to increase the amount of RAM while the VM is running, but it does not allow reductions.

WHY POWERING OFF IS RECOMMENDED:

As noted above, memory cannot be reduced on a live server and you can reduce the CPU count on a live server but it is not recommended because:

1. Stability: Making changes to the CPU configuration while the VM is running can lead to instability or unexpected behavior.
2. Proper Application: Some settings may not take effect until the VM is restarted, ensuring that the operating system and applications recognize the new configuration.
3. Avoiding Data Loss: Powering off the VM ensures that no data is being processed or written during the change, reducing the risk of data corruption.

If you need to make this change, it’s best to schedule a maintenance window to power off the VM, adjust the CPU settings, and then power it back on.

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