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Memory Utilization on VM

there is a VM that we have running in one of our clusters in vCenter. we have solarwinds monitoring the VMs and we have the Solarwinds virtualization manager plug-in. Solarwinds reports that a single VM is utilizing 98% of the 8 GB of memory and when you log onto the VM's operating system performance monitor, it reports the same statistics

When you view the performance for that VM in vSphere, it reports that the active memory is approximately 3.5 GB of memory but the Consumed memory counter does state that it is using close to all of the 8 GB. i'm curious why there is such a huge difference between what vSphere is reporting and what the VM and the monitoring software Solarwinds reports.

no end users are reporting any performance issues with that VM but that is not to say that there aren't any.

thanks
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David Johnson, CD

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jmcg

I'm disappointed to learn that SolarWinds doesn't do a better job of reporting this situation. I support David's explanation.

One of the things I liked most about VMware reporting was that it showed quite well how much or how little memory a VM needed to run properly, putting the lie to much rule-of-thumb sizing advice. If you see that a VM guest is consistently showing an "active memory" amount that is well below the amount of memory you've allocated, you're generally justified in trying the experiment of reducing its memory allocation.

Presented with "extra" memory, an OS or application (like SQL Server for a prime example) will "consume" it on the theory that some of the things it saves in memory will perhaps be useful in the future. That theory is okay when there's no other potential use for the memory, but the observation you can make with VMware's performance monitoring is that the memory is basically being wasted and you should consider making it available to some other VM whose workload will make more effective use of it.

For VM guests that are actively using all of their allocated memory, you can experiment with giving them more, but to perform the experiment properly, you'll need to have some way of measuring the workload's effective performance. Some workloads will use all available memory actively, but will have their actual performance limited by some other factor such as available disk IOPs - increasing the size of the working set might not increase performance at all.

jdilley

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thanks for the feedback David and jmcq. have some additional information that was just sent to me. please see the latest attachment. thanks

the text in the e-mail that accompanied the attachment is as follows:

Everyone,
This is what I find so odd. *** is showing memory pegged. And we have had a ton of conversations about that….  But look at the bottom of this screen grab. It looks like only a few CPU’s are being leveraged. In my mind, that is a problem. If the CPU’s were all hammered, then memory would be the next place for resources to be consumed? It is also odd that only two CPU’s show significant usage. Is there some way to spread this usage over the total amount of CPU’s?
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