# Calculating Disk Utilization

OpManager uses HostResource.mib and its OIDs to calculate the disk utilization for Linux and Windows based systems.

The SNMP response of the following OIDs are used to calculate the disk utilization:

1. `1.3.6.1.2.1.25.2.3.1.2` (hrStorageType)  
2. `1.3.6.1.2.1.25.2.3.1.4` (hrStorageAllocationUnits)  
3. `1.3.6.1.2.1.25.2.3.1.5` (hrStorageSize)  
4. `1.3.6.1.2.1.25.2.3.1.6` (hrStorageUsed)

OpManager uses the first OID (hrStorageType) to find the list of fixed disks and the next three OIDs will be used for actual calculation only for those fixed disks.

## How to query for these OIDs

Open CMD prompt as Admin and execute `mibbrowser.bat` under `/opmanager/bin`.

Load HostResources.mib and query the OIDs.

![Disk utilization calculation in OpManager: Execution of mibbrowser.bat in CMD prompt](https://www.manageengine.com/network-monitoring/how-to/images/DiskUtilization.png)

The formula for calculating disk utilization is:

### Percentage disk utilization = (Total disk used) * 100 / (hrAllocationUnits * hrStorageSize)

For example, from the above image, it can be seen that out of 6 instances first three are the actual fixed disks (partitions). Others are RAM info and removable disks. So we need to use only the first 3 instances for calculation.

Total used = 4096 * `31999148` + 4096 * `33167356` + 4096 * `36133897` = `414926442496` bytes = 386.43 GB

Total HD size = 4096 * `39551999` + 4096 * `40195071` + 4096 * `40195327` = `491284058112` bytes = 457.54 GB

So Disk Utilization = 386.43 * 100 / 457.54 = 84.45%