Virtual Machine Memory Usage

Monitoring and reporting for Veeam Backup & Replication, VMware vSphere and Microsoft Hyper-V

Virtual Machine Memory Usage

Veeam Logoby rogersillars » Fri May 25, 2012 8:07 am

Hi everyone

I'm sorry to ask this question again if someone else has already answered it.

I've been testing VeeamOne in order to take a look at our VM utilisation. The software is very good and makes our environment much more visible. However I’m still confused around the memory usage of our VMs. We have had the principal that if Windows needed 4GB of RAM we allocate that to the VM and ensure our hosts have enough physical memory at 1:1 ratio. We are now getting to a point of needing more memory or clawing back on allocated memory. I’m reluctant to do this if we reduce performance an increase paging to disk.

I read this article which seems good but it doesn't really give me an answer as to what to do.
http://craniumtales.blogspot.co.nz/2009 ... ained.html

For example we have a SharePoint server with 4GB of memory allocated:
Physical Memory (MB)
Total 4095
Cached 405
Available 414
Free 10

For the same VM VMware tells me
Consumed 4.07GB
Overhead Consumption 72MB
Private 4GB
Active 942MB

VeeamOne is telling me
Memory usage 850MB

It appears from the surface that we have allocated a significant amount of physical memory and are only using a fraction of it. What do I believe? Can I claim some of this memory back from the VMs?

Thanks,
Roger
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Re: Virtual Machine Memory Usage

Veeam Logoby Vitaliy S. » Fri May 25, 2012 10:51 am 1 person likes this post

Hi Roger,

VM memory usage is a percentage of currently used memory by the VM, as you can see from the screenshot it is calculated by dividing memory active by the machine memory amount. You cannot really compare the numbers taken from Task Manager and VMware, as there are many variables that can force Guest OS think that it is using maximum of allocated memory, while it might not be 100% true.

The point is that there are multiple memory management techniques that allow you to use more memory than you have on the physical host (memory sharing, memory compression, zipped memory etc,), this will all lead to discrepancy between Task Manager and VMware memory views. Moreover, if you configure resource reservations and limits for the VM, this will also lead to different utilization numbers.

See this similar topic for more details: Differences between Task Manager and Veeam

In addition to this, please note that some applications like SQL Server will consume all memory that was granted to the VM, but it does not mean that SQL Server needs more memory and you cannot reclaim it.

That said, if you want to know whether you can reduce configured memory amount or not, looking at real-time stats is not the best idea, as you might have a peak load that happens every time SharePoint users log on to the portal and start working with it, in this case you definitely need to reserve some amount of RAM to satisfy the peak memory demand.

If I were you, I would run an Oversized VMs report, that will analyze and show you the average and peak memory usage for the past week, month etc. Based on that figures you will see your average workload and figure our whether you can reclaim memory resources from this machine or not.

Sorry for the long post, but I've tried to cover as much details as possible ;)

Hope this helps!
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Re: Virtual Machine Memory Usage

Veeam Logoby rogersillars » Mon May 28, 2012 7:20 am

Hi Vitaliy

Thanks for your response. That give me something to go on.

Roger
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Veeam One and Windows task manager not same info

Veeam Logoby smitty-NED » Wed Jun 20, 2012 12:46 pm

[merged]

Hello Everyone,
A couple of weeks now I am working with Veeam One and I believe that the performance information isn’t correct. For example one of the VM’s is an SQL server with 7 Gb of memory, it always uses at least 3 Gb of memory or more when I look at the task manager. But when I look in Veeam One at the summary chart it’s a memory usage of around 450 MB, same info at the memory chart. Other VM’s same problem.
it looks like everything is working fine, no errors or warnings except that the info isn’t the same between Veeam One and Windows task manager. Does anyone has an theory how this is possible or how I can solve this.

The versions I have are:
Vmware vCenter: 4.1.0
all servers are virtual Windows 2008 R2 sp1
Veeam One 6.0

I appreciate any help.
thanks,
Rienk
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Re: Virtual Machine Memory Usage

Veeam Logoby jeremyh8 » Fri Jun 22, 2012 2:39 am

i would look at the same machine in virtual center and look at active memory. active memory is what i always go off of when seeing if a vm needs more memory or not. i bet active memory numbers and numbers in veeam one will be close. windows is just showing you what it thinks and what you care about is what vmware sees after its memory sharing and reduction techniques.
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Re: Virtual Machine Memory Usage

Veeam Logoby Vitaliy S. » Fri Jun 22, 2012 7:54 am

Absolutely correct.
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Re: Virtual Machine Memory Usage

Veeam Logoby lingeshwaran.r » Mon Aug 18, 2014 2:51 pm

I know its very old thread. But the below link will be very useful to understand VM memory usage.
http://www.unixarena.com/2014/07/calculate-vspheres-vm-memory-usage.html
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