SQLServer probe is returning incorrect space calculations for the following metrics:
The space calculations may be inaccurate, empty or display negative values.
This is due to the sp_spaceused system stored procedure returning incorrect data. This is most common when the database has had Data Definition Language (DDL) modifications, such as CREATE, ALTER, or DROP statements.
SQLServer 2008 - 2014.
Run the following command to recreate the statistics for the database. Note this can take some time to run on large tables or databases.
DBCC UPDATEUSAGE (DatabaseName)
DBCC UPDATEUSAGE (CA_UIM)