Reduce the size of Monitoring database

How do I reduce the size of the Monitoring Database folder?

By default, historic data (in monitoring database) are kept for 365 days. If you want to keep less monitoring data on the hard disk, you can change the automatic data purging limits: please click on Setup | System Administration | Core & Probes, scroll down to Historic Data Purging and under Historic Sensor Data, you can change for how many days historic data will be kept.

To generally save disk space, enabling the NTFS compression for the PRTG data directory is usually a good option. Because in modern Windows versions, this does not drain performance, but saves a lot of disk space.

Or move the data directory to another larger hard drive: https://kb.paessler.com/en/topic/543-how-can-i-change-the-data-directory-of-my-prtg-installation

Please note that we strongly advise against PRTG files and database being stored on network shares. We see frequently write/read locks and other performance issues that happen on installations whose configuration files and databases are on a network location. Due to the type of I/O PRTG is producing, there is a huge amount of individual read/write operations that can affect performance on network shares, so we strongly recommend to keep these files locally on the server.