vSphere 6 ESXi memory states and reclamation techniques

vSphere 6 uses the well known memory reclamation techniques you may already know from previous versions:

• transparent page sharing (TPS)
• memory ballooning
• memory compression
• memory swapping

The memory reclamation technique that is used depends on the ESXi host memory state, which is determined by the amount of free memory of the ESXi host at a given time.

With vSphere 6 VMware introduced a new memory state, called “clear state“.

So vSphere 6 knows five different memory states associated with one or more memory reclamation techniques to reclaim memory:

But which treshold of free memory is associated with which memory state?

ESXi uses a value called “minFree” for the memory state calculation. minFree is a dynamic value and depends on the ESXi host memory configuration.

You can calculate minFree very easy for your ESXi host:
for the first 28 GB of physical RAM in the ESXi Host: minFree = 899 MB
+ add 1 percent of the remaining RAM to your calculation

Figure: „minFree calculation example vSphere 6:

In the example above the ESXi host has 100 GB memory:
for the first 28 GB RAM minFree = 899 MB, for the remaining 72 GB (100 GB – 28 GB) we have to add 1% to minFree: 1% of 720 GB = 720 MB -> minFree is 899 MB + 720 MB = 1619

Thresholds:

• high state: enough free memory available
• clear state: <100% of minFree
• soft state: <64% of minFree
• hard state: <32% of minFree
• low state: <16% of minFree

If you want to know the memory state of one of your ESXi hosts you can use ESXTOP (extract from the vSphere 6 ESXTOP quick Overview for Troubleshooting” diagram):

Open ESXTOP and type “m” for the memory tab. The host memory state is displayed in the first line on the right.

You want to learn more about ESXTOP?

Take a look at the vSphere 6 ESXTOP quick Overview for Troubleshooting” diagram: