The Memory Swapout chart displays the swapout memory usage for fault tolerant virtual machines.

This chart is located in the Fault Tolerance view of the Virtual Machine Peformance tab. It is not available at collection level 1.

Table 1. Data Counters

Chart Label



Amount of machine memory written to the VMkernel swap file.

  • Counter: swapout

  • Stats Type: Absolute

  • Unit: MegaBytes

  • Rollup Type: Average (Minimum/Maximum)

  • Collection Level: 2 (4)

Make sure that the primary and secondary virtual machines have enough memory and that the swapout value is not high. If the secondary system is not provisioned well, it might slow down performance of the primary virtual machine or fail.

Chart Analysis

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 there is sufficient swap space, a high balloon value is not a performance issue. However, if the swapin and swapout values for the host are large, the host is probably lacking the 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. The host might require more memory resources. If it does not, 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 memory usage is high or you notice degredation in performance, consider taking the following actions.

Table 2. Memory Performance Enhancement Advice




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 a 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.