vSphere 5: Memory share calculation for mem.minfreepct
While I was reading up the vSphere 5 Clustering Technical Deep Dive book by Duncan Epping and Frank Denneman, I came across this section which took me to awhile to understand the calculation for the math part.
This section on memory share which has been changed in vSphere 5 which is also written in Frank Denneman, Mem.MinFreePct sliding scale function.
The example is as below:
Let’s use an example to explore the savings of the sliding scale technique. On a server configured with 96GB RAM, the MinFreePct threshold will be set at 1597.6MB, opposed to 5898.24MB if 6% was used for the complete range 96GB.
I was trying to get the calculation for the Result column and thought to elaborate it on a clearer picture which a believe some are confused like myself.
The first 0-4GB will be on 6%, followed by from 4GB-8GB will be 4%(which is total of 4GB), then the next 12GB-28GB on 2% (which is 16GB) and lastly the remaining memory minus off from total on 1% (which is 68GB). When you add those up would give you the Threshold.
Hope that helps how the math was derived.
This section on memory share which has been changed in vSphere 5 which is also written in Frank Denneman, Mem.MinFreePct sliding scale function.
The example is as below:
Let’s use an example to explore the savings of the sliding scale technique. On a server configured with 96GB RAM, the MinFreePct threshold will be set at 1597.6MB, opposed to 5898.24MB if 6% was used for the complete range 96GB.
| Free memory state | Threshold | Range | Result |
| High | 6% | 0-4GB | 245.96MB |
| 4% | 4-12GB | 327.84MB | |
| 2% | 12-28GB | 696.32MB | |
| 1% | Remaining memory | 696.32MB | |
| Total High Threshold | 1597.60MB |
I was trying to get the calculation for the Result column and thought to elaborate it on a clearer picture which a believe some are confused like myself.
The first 0-4GB will be on 6%, followed by from 4GB-8GB will be 4%(which is total of 4GB), then the next 12GB-28GB on 2% (which is 16GB) and lastly the remaining memory minus off from total on 1% (which is 68GB). When you add those up would give you the Threshold.
Hope that helps how the math was derived.
Comments
So changing the Mem.MemMinFreePct-setting to 10 % would, following the above assumption, result in:
Range %
4-12 GB => 6 % (64 % of 10 %)
12-28 GB => 3 % (32 % of 10 %)
remaining => 1.6 ~ 2 % (16 % of 10 %)
Is this assumption correct? Or how does it work?
Thanks on advance!
http://www.yellow-bricks.com/2013/06/14/how-does-mem-minfreepct-work-with-vsphere-5-0-and-up