As a rule of thumb, we can say that WMI sensors need up to 10 times more resources than SNMP sensors. This is because of the architecture of these technologies. This means that you should be careful when setting up many WMI sensors and you should prefer SNMP sensors when possible.
Please understand that we cannot provide you with fixed numbers, due to the individual behavior of WMI in different configurations. You can refer to the manual section Detailed System Requirements for guidelines.
Please note two other hints regarding OS and intervals below.
Generally, the WMI performance depends on the operating systems used. From our experience, you should use the following systems (in order of performance):
- Windows Server 2003
- Windows Server 2008 R2
- Windows XP
- Windows 7
Please see also How can I speed up PRTG - especially for large installations?
The WMI performance also depends very much on the scanning interval you select—the bigger the interval, the more sensors you can set up. This is because WMI sensors can only overload a system when they're in action. So, if you experience your system being slow when adding many WMI sensors, try using larger intervals.