When it comes VMware memory monitoring – two items to monitor (i)ESXi host memory (ii)VM memory. There are bunch of memory related terminologies and calculations here in this space. I am discussing host memory monitoring here –
-understand physical memory usage monitoring
-what is the right memory counter to monitor & alert notification for esxi host
-what is the right gauge of memory monitoring & alert notification for esxi host
Will also setup Nagios check plugin to monitor the above with performance data for graph (Part 2).
Before moving forward; let’s have a look into Mem.MinFreePct function. This function manage how much host memory should be kept free and when the hypervisor should kick-off advanced memory reclamation techniques such as ballooning, compression, swapping.
(Configuration> Advanced Settings>Mem)
Based on free host memory & reclamation techniques – there are four (04) different states of host memory utilization;
| State Name | Mem Reclamation Technique | Good or Bad | Note |
| High | At this state “Transparent Page Sharing” is will be always running. This is default behaviour. | Good – this is normal | This is defined by Mem.MinFreePct function. Don’t disable TPS – not recommended. |
| Soft | At this state host will activate memory ballooning. | Not good enough | This is 64% of Mem.MinFreePct. This means physical memory near to max out. If host unable to go back to previous state itself – take necessary action to free up more mem. |
| Hard | At this state host will start doing memory compression and hypervisor level swapping. | Bad – memory under stress | This is 32% of Mem.MinFreePct. Need to free up memory by migrating VMs to other hosts or upgrade memory. |
| Low | At this state host will no more serve any page to VMs. | Very Bad – fix it ASAP | This is 16% of Mem.MinFreePct. This protects host VMkernel layer from Purple Screen of Death. |
Prior to ESXi-5.x this (high state) was set to 6% by default – this means host system will always keep 6% of total physical memory free before activate advanced memory reclamation technique; let’s say an ESXi-4.x host with 64GB memory will be required at least 3.84GB free to be in the High state (normal).
Starting from ESXi-5.x this calculation is no more 6% by default – because high memory servers (512GB/768GB) are becoming common these days; 6% of 512GB is 30.72GB its huge free memory.
The new calculation is following –
| Free Memory Threshold | Range | Calculation Note |
| 6% | First 0GB to 4 GB | 6% of 4GB |
| 4% | Starting from 4GB to 12GB | (12-4=8) 4% of 8GB |
| 2% | Starting from 12GB to 28GB | (28-12=16) 4% of 16GB |
| 1% | Remaining memory | i.e. 36GB if total size is 64GB (64-28=36) i.e. 68GB if total size is 96GB (96-28=68) |
Based on above – on a system with 128GB memory, the min free memory required to be in “high state” calculation is following –
i. 6% of first 4GB – this is 245.76MB (first 0-4GB)
ii. 4% of 8GB – this is 327.68MB (0-4GB|4-12GB)
iii. 2% of 16GB – this is 327.68MB (0-4GB|4-12GB|12-28GB)
iv. 1% of 100GB – this is 1024MB (0-4|4-12|12-28|28-128GB)
v. Total is 1925.12MB (245.76+327.68+327.68+1024).
Based on the above we can setup monitoring & alert notification for a 128GB host as following –
| Mem State | Min Free Mem | Monitoring Action | Calculation |
| High | 1925.12MB | No action required | Based on above |
| Soft | 1232.0768MB | Warning alert | 64% of Mem.MinFreePct |
| Hard | 616.384MB | Critical alert | 32% of Mem.MinFreePct |
| Low | 308.0192MB | Critical alert | 16% of Mem.MinFreePct |
Also at “Hard” state – memory performance measurement counter “Swap used” will be greater than 0. This condition also should trigger alarm.
(esxtop – memory high state)
References:
http://blogs.vmware.com/vsphere/2012/05/memminfreepct-sliding-scale-function.html
iCookServers-&-Networks 