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I am working on the sizing for a virtual server to be used for Business Intelligence ETL processing.

We have an existing server from which I can observe the expected trend on the planned one - almost 80% RAM (of 8GB) is used on average and page file usage varies greately based on the batch job being processed.

Now going for a virtual server option - should I estimate more than the existing RAM like 12GB or so and disable paging? Since I'm afraid excessive paging will cause performance issues on a virtualised server, compared to the same amount of paging being done on a normal machine.

Is it recommended to set lower paging space and ask for more memory allocated on the virtual server, if there is chance of excessive paging -since the application is a data crunching one?

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  • What virtualization hypervisor technology are you planning to use? – ewwhite Feb 4 '13 at 13:50
  • Unfortunately I can only assume at the moment it is VSphere, this part is handled by another team. Does the platform really make a difference in the sizing decision? – dbza Feb 4 '13 at 14:40
  • Yes. Yes it does. – ewwhite Feb 4 '13 at 14:41
  • Update: the plan is dropped because there was an opinion that use of a VM for ETL could cause performance issues due to high data input/output operations. – dbza Feb 16 '13 at 9:31
  • That's unfortunate. We've evolved to the point where virtualized systems can run with little or negligible performance impact. This all depends on design, of course. – ewwhite Feb 16 '13 at 16:48
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In this case, I would plan for the amount of RAM you really need, plus some... Say 16GB. In the example of VMware, there is a swap file created per VM, but the system behavior when RAM is exhausted depends on the underlying hardware and the manner in which the host/cluster was configured.

You didn't specify the operating system in use either, but don't disable paging/swap.

The other benefit of going virtual... it is trivial to adjust the RAM allocation if there are problems down the line.

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