tekhie
Contributor
Contributor

A question around consumed and active memory

Hi - i am looking to review memory allocations to VM's as im sure that some have been given too much previously.We have a policy of no overcommitment of RAM so before i buy more i want to review what is currently used.

For the VM metrics  i would like to clarify the following ...

I have a VM that has been configured with 4GB RAM

The Consumed Host Memory value is 2869MB

The Active Guest Memory value is 327MB

So my question is as follows ... is the VM consuming 2869MB just becuase it can ? Even though it is only activley using 327MB

If i was to reduce the memory allocation by half for example, woud that have a negative impact on performance ? or would it just mean that the vm would consume less memory and still only actively use around 327MB ? Im trying to understand the correlation between configured memory, consumed memory and active memory

Any advice would be most welcome.

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5 Replies
idle-jam
Immortal
Immortal

configured is what you have assigned to the virtual machine, active are those current use by the OS and consume are "reserved" for the virtual machine usage. it does make sense to go lower with no performance impact but then what you might be looking now is the point in time report. you may need tools to look over period of says 2 weeks and 4 weeks to know what is a good number to down size.  btw, if there is a memory constraints and that another VM requires more active memory, memory balloning from vmware tools would free up some of the RAM in the consumed and pass it to the VM that requires active memory. all this is done automatically.

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tekhie
Contributor
Contributor

hi thanks very much for the response - it pretty much confirms what i expected.  When looking at the last 4 weeks memory stats the values are as follows :

Consumed - maximum value = 3.2GB

Active - maximum value = 0.95GB

Active - average value = 491MB

VM is granted 4GB

I am pretty confident that i can drop the configured RAM down to 2GB and suffer no performance impact

just out of interest - what is the usage %  vlaue based on ? from the stats above it seems to roughly equate to the active memory as a % of the granted. Is this assumption correct ?

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rickardnobel
Champion
Champion

idle-jam wrote:

configured is what you have assigned to the virtual machine, active are those current use by the OS and consume are "reserved" for the virtual machine usage.

Is that really so? Is not consumed the amount of RAM that the guest has loaded something into, i.e. is actually using in form av some loaded services, applications and so on, and the active is an estimated amount of how much of the memory that the guest quite recently has been using.

So a guest might start up, load loads of drivers, services and different programs into, say 1 GB of RAM, but when doing its normal duty perhaps just 256 MB of these memory pages is often used. However, if the VM was given only 512 MB it might work extremly bad due to internal guest swapping.

My VMware blog: www.rickardnobel.se
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EricJackson2011
Contributor
Contributor

Hi,

We just recently had one of our technical team do a whitepaper on memory management metrics for VMware environments and how to use them for sizing - you may find it helpful. You can get it here: http://www.vkernel.com/resources/whitepapers.

Eric Jackson

VP Product Management, VKernel

http://www.vkernel.com

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bilalhashmi
Expert
Expert

Tekhie,

This might help you answer your questions as Duncan explained it.

Follow me @ Cloud-Buddy.com

Blog: www.Cloud-Buddy.com | Follow me @hashmibilal
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