VMWare CPU Limit effect on VM computing and disk speed – CPU stolen time

Symptoms:
Customer complaining about slow SQL server and event application timeout.
Hihg CPU usage and slow disk with bad disk time response.
Let’s check the the 4 CPU core:
Hihg CPU usage at night

At first glance, it seemed like a heavily used server.
The lack of server resources caused timeouts for the applications.

I suspect VMWare virtualization cause performance issue:

VMWare Virtualization CPU Stolen time
CPU Stolen time is high

Thanks for the teamwork, we found the settings which caused a poor performance:

CPU Limit is low
CPU Limit is low

To set new value in VMWare:

CPU Limit is low
CPU Limit is UP

After changing the limit the performance increased.
See the before and after (left and right columns) performance monitor reports:

VMWare Speed limited , CPU usage and disk response time
VMWare Speed in Limited , CPU usage and disk response time before and after
SQL query require less time after changes
SQL query requires less time after changes and even the disk IO is increased

Finally a simple performance example for the backup job:

SQL server backup job times
SQL server backup job times

 

Conclusion:

Heavy usage symptoms can be misleading in the VM.

Useful perf counters:

CPU “Limitation”, has a big effect to CPU and DISK performance, which is almost hidden in a VM guest.

Some tips for you, if you suspect poor performance:

  • check disk response time in resource monitor
  • check performance monitor counters
  • have a baseline

 

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