Saturday, September 17, 2011

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.
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


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.
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