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
- 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: