Linux Guests Poor Performance

[LM_Chris]

I have a number of admins telling me that their CentOS 5 guests are showing signs of poor performance. Simple things like "ls" seem to take a long time. I've made sure that they updated their vmware tools installation following kernel updates. The ESX hosts show nothing to help us trouble shoot this problem. both CPU and memory usage on the guests are low. CPU and memory usage on the hosts are low as well. The Windows boxes that share the same host do not show any problems.

We are using Vintela and I wonder if there is some sort of time/authentication problem occuring. Should I be doing something with NTP?

[smokey71]

Hello,

You can try setting 896MBs of RAM due to mapping techniques that Linux uses. That may help performance a bit.

http://www.vmware.com/pdf/vi_performance_tuning.pdf

"If possible, use less than 896MB of guest physical memory on Linux virtual

machines. Linux uses different techniques to map memory in the kernel if the

amount of physical memory is greater than 896MB. These techniques impose

additional overhead on the virtual machine monitor and can result in slightly

lowered performance."

Also, I have noticed in the past that having the VM sync time with the ESX host causes issues. In our environment we set our servers to sync with the domain's NTP server. You may want to consider testing that if you sync VM's to your ESX hosts via VMware tools.

/r,

Smokey

[AlbertWT]

Yes, and also make sure that the VMware tools is installed and running.

Kind Regards,

AWT

[LM_Chris]

All the guests have 2GB of RAM allocated and I am not seeing much being used. I also don't see much CPU being used. We just did a test and determined performance is normal right after a boot-up. I wonder if there is some CPU power-saving features happening on the guests and they never leave that state?

[RParker]

All the guests have 2GB of RAM allocated and I am not seeing much being used.

It doesn't matter the AMOUNT of RAM being used or allocated, it HOW Linux techniques work that causes the issue. Try setting the VM to LESS than 896Meg of RAM, just to SEE if it makes a difference.

If it does.. there is your answer. So the next step is to let your users know it's a known issue.. they may need more than 2GB of RAM, if that's true and the performance isn't adequate, then maybe VM's won't work for your scenario.