Unable to hot-add memory to VM

Products

• VMware vCenter Server

Issue/Introduction

Typically this can happen when you try to add a small amount of memory to a VM. Addition of larger amounts of memory can complete without issue.

hostd.log contains the following:

Reconfigure failed: N3Vim5Fault20GenericVmConfigFault9ExceptionE(Fault cause: vim.fault.GenericVmConfigFault

 

vpxa.log contains:

--> (vim.fault.GenericVmConfigFault)

...

-->          message = "Unknown error."

 

vmware.log for the VM contains the following:

vmx - memoryHotplug: Change of memory size from XXXXX to YYYYY was requested

vmx - memoryHotplug: Please increase guest size to at least ZZZZZZMB to trigger hotplug event

 

Environment

vCenter Server 7.0

vCenter Server 8.0

ESXi 7.0

ESXi 8.0

Cause

This is expected behaviour.

Resolution

To determine the minimum amount of memory required to be added, perform the following steps:

Determine the Vmid of the VM:

vim-cmd vmsvc/getallvms

Using the Vmid from the previous output, execute the following:

vim-cmd vmsvc/get.config <Vmid> | grep hotPlugMemoryIncrementSize

An output of, for example, "hotPlugMemoryIncrementSize = 128" would mean that memory can only be added to the VM in increments of 128 MB.