Host Memory Usage

Host Memory usage alarm VMware

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We have seen the VMware ESXi host memory usage alarm in the vSphere console many times during the operations. Today we will discuss what course of action can be taken to remediate this issue.

The ESXi host memory usage go to high when the hosted Virtual Machines utilize higher memory than usual may be during specific job like backup job.

You can clear the alarm or monitor it. It will come to normal stage after sometimes. Alternatively you can either increase the RAM size of that esxi host or add more host in the cluster to balance the resource utilization.

How to clear the Alarm

To clear warnings and errors from the Hardware Status tab:

  1. Go to the Hardware Status tab.
  2. Click the System event log view.
  3. Click Reset event log.
  4. Click Update. The error clears.
  5. Click the Alerts and warnings view.
  6. Click Reset sensors.
  7. Click Update. The memory clears.

Virtual machine memory

We can work with the virtual machine also. A virtual machine’s memory size must be slightly larger than the average guest memory usage. This enables the host to accommodate workload spikes without swapping memory among guests. Increasing the virtual machine memory size results in more overhead memory usage.

If sufficient swap space is available, a high balloon value does not cause performance problems. However, if the swapin and swapout values for the host are large, the host is probably lacking the amount of memory required to meet the demand.

If a virtual machine has high ballooning or swapping, check the amount of free physical memory on the host. A free memory value of 6% or less indicates that the host cannot meet the memory requirements. This leads to memory reclamation, which might degrade performance. If the active memory size is the same as the granted memory size, demand for memory is greater than the memory resources available. If the active memory is consistently low, the memory size might be too large.

If the host has enough free memory, check the resource shares, reservation, and limit of the virtual machines and resource pools on the host. Verify that the host settings are adequate and not lower than those set for the virtual machine.

If little free memory is available, or if you notice degradation in performance, consider taking the following actions.

  • Verify that VMware Tools is installed on each virtual machine. The balloon driver is installed with VMware Tools and is critical to performance.
  • Verify that the balloon driver is enabled. The VMkernel regularly reclaims unused virtual machine memory by ballooning and swapping. Generally, this does not impact virtual machine performance.
  • Reduce the memory space on the virtual machine, and correct the cache size if it is too large. This frees up memory for other virtual machines.
  • If the memory reservation of the virtual machine is set to a value much higher than its active memory, decrease the reservation setting so that the VMkernel can reclaim the idle memory for other virtual machines on the host.
  • Migrate one or more virtual machines to a host in a DRS cluster.
  • Add physical memory to the host.

This way you will be able to resolve the issue of VMware host memory usage.


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