The SQL Server Tablespace Check monitor connects directly to the database instance and runs the following set of commands to verify tablespace usage:


sp_helpdb $name;

A warning or critical outage will be registered if any database is outside the monitor thresholds.

If your database uses Unlimited max size values, they will not be included in the tablespace check.  In this case it is often more appropriate to use the File System Capacity monitor to check the overall usage on the volume hosting your database.