How can I monitor disk I/O speed?

Can you help me to add custom WMI monitors?

Q: Can you help me to add a custom WMI monitor? For example, what query can be used to check disk C: Read & Write Bytes per Sec?

A: The following custom WMI Query can be used:

SELECT DiskBytesPerSec FROM Win32_PerfFormattedData_PerfDisk_LogicalDisk WHERE Name = "C:"

In general, if you need to read a Windows performance counter value, you should

  1. Find the corresponding Win32_PerfFormattedData-derived WMI class:
    http://msdn.microsoft.com/en-us/library/aa392397
    http://msdn.microsoft.com/en-us/library/aa394253
  2. Choose the needed class property (properties correspond to counters). For example, properties of Win32_PerfFormattedData_PerfDisk_LogicalDisk class can be found at:
    http://msdn.microsoft.com/en-us/library/aa394261
  3. Construct the WMI Query as 
        SELECT <property name> FROM  WHERE Name = <instance name>

    Note: WHERE clause is required if there are several instances (e.g. if several logical disks are configured)

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Frequently Asked Questions

Check out our Knowledge Base where we answer questions regarding various topics.

Which WMI query can monitor C: disk read and write bytes per second?

Use SELECT DiskBytesPerSec FROM Win32_PerfFormattedData_PerfDisk_LogicalDisk WHERE Name = “C:” to read the combined disk bytes per second value for drive C:.

How do I choose a WMI class for a Windows performance counter?

Find the Win32_PerfFormattedData-derived class that corresponds to the Windows performance object, then select the property that matches the counter you want to monitor.

Why is a WHERE clause often needed in a WMI performance query?

A WHERE clause selects the correct instance, such as a specific logical disk, when the WMI class can return several instances.