Why Does Monsta Show a Partition with 5% Less Used Space?

This 5% difference in the disk space of a Linux partition, when monitored via SNMP, is a standard characteristic of the Ext2, Ext3 and Ext4 filesystems. It is not a miscalculation, but an intentional space reservation.

This reservation exists to ensure the system continues to operate stably, even when the disk is nearly full. The 5% is reserved primarily for the root user, the system administrator.

The main reasons for this reservation are to:

• Prevent file fragmentation: The reservation helps ensure the filesystem has enough space to allocate new data contiguously, which improves performance.
• Allow the system to operate: If the disk fills to 100%, the operating system can hang or become unusable. This reservation ensures that root has space to, for example, write logs, move files, or run essential commands to free space.

In summary, the 5% difference is a feature of the Ext filesystem designed for protection. It ensures the administrator always has a buffer to perform critical operations and maintain the server’s stability.