Guest RAM performance

[ashleyholland]

Hello,

I am experiencing a problem with a slow guest and have been completing some performance tests and notice that the RAM performance seems to be poor. The Host server is a DELL R715 with 2 AMD 6212 processors and has 64 G of DDR3 RAM. I currently only have a single guest machine running W2k8 configued with 1 socket and 2 cores and 4G of reserved memory so we are not overloading the system. The hard disks on the guest  a using the hosts disks (we have disk array connected but I did not want to add this as a factor in the tests) and they have lots of free space.

I have run memtest on the server and no problems were reported.

I ran  PerformanceTest on the guest and it's memory score is very low (~400).  I created a test W7 guest and the results were also very low.

I also checked the BIOS settings on the server and all seems to be OK.

http://en.community.dell.com/techcenter/virtualization/w/wiki/dell-vmware-vsphere-performance-best-p...

Does anyone have some advice as how to investigate this further ?

Thanks in advance,

Ashley

[JCMorrissey]

Hi,

Have you looked into testing using a memory reservation for the VM? good article discussing the piece too

http://frankdenneman.nl/2009/12/08/impact-of-memory-reservation/

Also, not sure if this a pre-production box but if it isnt if you install Windows bare-metal do you see the same performance issues

[marcelo_soares]

I don t believe it can be this, but try to disable page sharing for this specific machine. Check http://pubs.vmware.com/vsphere-4-esx-vcenter/index.jsp?topic=/com.vmware.vsphere.resourcemanagement.... on how to do it:

"You can also disable sharing for individual virtual machines by setting the sched.mem.pshare.enable option to FALSE (this option defaults to TRUE). See Set Advanced Virtual Machine Attributes."

Check if this works. Also, check if you don't have any limits on the VM CPU/Memory.

[ashleyholland]

Hi And thanks for your replies. I re-checked the BIOS settings in the host and not all the Power parameters were set to Maximum performance, so I changed this and I also re-enabled the SE1 setting because disabling seemed to degrade the performance. I am getting much improved performance more consistent with the physically hardware

Disabling paging did not seem to make any difference, but I think that the problem was due to the BIOS settings. I will now try to change the setting on our production server and see if we get the same performance improvement.

Kind regards,

Ashley

[marcelo_soares]

Sure, you nailed it. This kind of config can slow down your system. At the end, no RAM problem at all.

Good luck with your production!

Marcelo

twitter: @mtsoares42