6.5.1

Chart Analysis
To ensure best performance, the host memory must be large enough to accommodate the active memory of
the virtual machines. The active memory can be smaller than the virtual machine memory size. It allows you
to over-provision memory, but still ensures that the virtual machine active memory is smaller than the host
memory.
Transient high-usage values usually do not cause performance degradation. For example, memory usage
can be high when several virtual machines are started at the same time or when a spike occurs in virtual
machine workload. However, a consistently high memory usage value (94% or greater) indicates that the
host is probably lacking the memory required to meet the demand. If the active memory size is the same as
the granted memory size, the 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 memory usage value is high, and the host 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 handle the
demand for memory. It leads to memory reclamation, which might degrade performance.
If the host has enough free memory, check the resource shares, reservation, and limit seings of the virtual
machines and resource pools on the host. Verify that the host seings are adequate and not lower than those
set for the virtual machines.
If the host has lile free memory available, or if you notice a degradation in performance, consider taking
the following actions.
Table 1‑66. Memory Performance Enhancement Advice
# Resolution
1 Verify that VMware Tools is installed on each virtual machine. The balloon driver is installed with VMware Tools
and is critical to performance.
2 Verify that the balloon driver is enabled. The VMkernel regularly reclaims unused virtual machine memory by
ballooning and swapping. Generally, it does not impact virtual machine performance.
3 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.
4 If the memory reservation of the virtual machine is set to a value much higher than its active memory, decrease the
reservation seing so that the VMkernel can reclaim the idle memory for other virtual machines on the host.
5 Migrate one or more virtual machines to a host in a DRS cluster.
6 Add physical memory to the host.
Memory Usage
The Memory Usage chart displays memory usage for the 10 virtual machines on the host with the most
memory usage.
This chart is located in the Virtual Machines view of the host Performance tab.
Virtual Machine Counters
N Guest physical memory refers to the virtual hardware memory presented to a virtual machine for its
guest operating system.
vSphere Monitoring and Performance
50 VMware, Inc.