Scott Drummonds on Virtualization

Optimizing Memory Utilization


My recent series of blog articles have discussed ESX memory management the the performance specter of host swapping. My last article attempts to correct the misconception that VMware recommends against over-commit memory.  In that article I suggested that memory over-commit is requirement in optimizing memory utilization. Today I want to provide a specific example to show why this is true.   I am have also included tips for identifying host swapping in your environments.
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Misunderstanding Memory Management


Twice in 2009 someone showed me competitive literature from Microsoft or Citrix claiming that VMware recommends against memory over-commitment.  Given the wide variety of literature we have provided in support of this feature, all of our customers recognize the absurdity of our competitions’ claims.  VMware and its customers love memory over-commitment.  Then where is the source of this misinformed guidance?

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Solid State Disks and Host Swapping


Recently I have been thinking, talking, and writing about ESX host memory swapping a lot.  ESX swaps memory under the same conditions that traditional operating systems do; the application(s) is using more memory than available on the physical hardware.  Host swapping is an unavoidable consequence of this condition, whether virtualization is present or not.

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Your Performance Enemy: Host Swapping

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Three times in the past week I have engaged in challenging discussions on host memory swapping and its impact to performance.  If you read my article on host swapping and the whitepaper it summarized, you know the deleterious effect on performance caused by host swapping.  When reading the paper, one of our most astute customers saw a sentence that gave him pause:
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