Memory alarm. vSphere Host memory 100% reported. Guest task manager says 50% used. (?)

[Valamas]

Hello,

We have virtual machines showing in vSphere that 100% of their memory is being used. An alert symbol is displaying. However, when we RDP into the machine and view the memory usage; it is showing normal usage.

We are using brand new Dell R710 servers with 32 GB of memory, dual Quad Core E5530 Xeon.

With the number of virtual machines we have on there, we have plenty of server memory left (no over allocation). Also, currently the virtual machines are not being utilised and sit on near zero CPU as we continue to set them up. The memory alarm concerns us and we want to make sure there is nothing wrong.

One change we have made that seems to have alleviated/delayed the alarm showing is that we have changed the paging file size to be windows managed in the guest. However, the problem of memory alarm seems to be occurring at what seems to be a slower eventuation.

Other than NTbackup and Windows Server 2008 backup and local sql backups in the early morning hours, nothing much is going on with these machines.

I have posted a set of print screens showing the memory of a single machine showing the alarm this morning.

This machine is Windows 2008 + Sql 2005 w/ 1280 ram. It is not under any other load as it is still being setup. A non-commissioned prod version of this machine with 2048 ram also displays the memory alarm after a time. Again, not under load yet.

Other machines which show the alarm have either Win2008 or Win2003.

I have posted an image showing the memory usage reported in vSphere and in the guest.

Appreciate any help and please let me know if I can provide any more information.

cheers,

Mike

[Valamas]

The following thread and testing has helped up understand memory usage.

http://communities.vmware.com/thread/120848

[tracylbrown]

We have noticed the exact same thing. However, we have seen it in both our Windows and Linux VMs. Vcenter reports the alarm but when you look into the VM the OS is showing far less memory being used to what Vcenter is reporting being used. The thread given to look at states that Windows touches all the memory at boot up and causes the false report. We are however seeing the same with Linux VMs. What good is the alarm if this is true? Can the alarm be disabled all together? Is that wise?

--tracy

[Valamas]

Hi Tracy, we were discussing the same thing about the alarm. We have elected to ignore them (at our peril?!).

We tried to disable them, but they still appear. Ignore seems to be the only option.

cheers,

[mcwill]

Hi,

What you are seeing is due to an inability of vsphere to track memory usage when hardware accelerated large pages are used.

http://communities.vmware.com/thread/211585

A fix is promised from vmware with Update 1 of vsphere. If you wish the memory tracking can be corrected by disabling one of the above features, (details in the linked thread) but this will affect performance.

Regards,

Iain

[Valamas]

Thank you very much for posting that thread to me.

[tracylbrown]

Lain,

Thanks for the link. This is the information I was needing.

--tracy

[ealaqqad]

Hi All,

The fix for this issue has been released a while back in case any one still read this post.

If you want more information of the fix & this problem you can find more information by reading my following post

Guest operating system’s memory usage might be overestimated on VMware ESX 4

I hope this help some one, if it does please reward points.

Enjoy,

Eiad Al-Aqqad

System X & Storage Technical Specialist

Founder of http://www.VirtualizationTeam.com