Windows Guest OS shows limited usable memory despite increasing VM memory in ESXi

Products

• VMware vSphere ESXi 8.0

Issue/Introduction

After increasing the virtual machine (VM) memory allocation in the ESXi host, the Windows guest operating system displays the correct total installed memory (e.g., 48 GB) but shows only a small portion as usable (e.g., 2.00 GB usable).

 

Environment

VMware vSphere ESXi: 7.x

VMware vSphere ESXi 8.x

 

Cause

This issue occurs within the Windows guest operating system. Even though the ESXi host has correctly allocated the increased memory, the guest OS may restrict its usable memory due to internal configuration or a process reserving the memory.

Resolution

To remediate the issue, follow the below steps

Step 1:

• Verify Memory Allocation from ESXi Host
• SSH into the ESXi host.
• Run the following command to list the VMs and identify the VM ID:
• vim-cmd vmsvc/getallvms | grep <vmname>
• Check the memory summary for the VM:
• vim-cmd vmsvc/get.summary <vmid> | grep memory
• Confirm that the increased memory is reflected correctly.
• Also, verify that no memory reservation is configured at the VM level in vSphere Client.

Step 2:

• Check Guest OS Configuration
• Inside the Windows guest OS, press Windows + R, type msconfig, and press Enter.
• Navigate to Boot → Advanced Options.
• Verify if Maximum Memory is checked.

Step 3:

• If checked, uncheck it and restart the VM.
• This ensures the OS can utilize the full allocated memory.

 

If the above checks confirm that the ESXi configuration and VM settings are correct, contact the Guest OS vendor (Microsoft) for further troubleshooting at the OS level.

 

Additional Information

This is not an ESXi or vSphere issue if the allocated memory is correctly reflected in the host and VM configuration.

Always ensure VMware Tools are up to date before performing further analysis.