This article applies to PRTG Network Monitor 12 or later

Logical and Physical Disk Monitoring

The two sensors monitor different counters provided by the Windows system running on a computer, all regarding the performance of available the hard disk drives.

WMI Logical Disk

This sensor can monitor the logical partitions which are available on a fixed disk drive. Logical disk instances are identified by the drive letter, such as C.

Among the available counters are:

• Free Space (% and Total)
• Disk Queue Length (Read / Write)
• Disk Time
• Avg. Disk sec/Transfer

For detailed information, please see the description in MSDN: Win32_PerfFormattedData_PerfDisk_LogicalDisk Class

Windows Physical Disk

This sensor can show raw data from performance counters that monitor hard or fixed disk drives on a computer. For this purpose, this sensor type uses a hybrid approach, first trying to query data via Windows Performance Counters (which needs less system resources), and using WMI as a fallback in case performance counters are not available. In previous PRTG versions, this sensor used WMI only and was called WMI Physical Disk Sensor.

Disks are used to store file, program, and paging data and are read to retrieve these items, and written to record changes to them. The values of physical disk counters are sums of the values of the logical disks, or partitions, into which they are divided.

Among the available counters are:

• Disk Read/Write Time
• Idle Time
• Avg. Disk Read/Write/Transfer
• Disk Queue Length (Read / Write)
• Split IO/Sec

For detailed information, please see the description in MSDN: Win32_PerfRawData_PerfDisk_PhysicalDisk Class