The Filegroup Space Full (Percent) alert provides the percentage of the allowable filegroup space for the database currently used by all files within the filegroup. Allowable disk space for the database is calculated by taking into account the current allocated space, SQLdm auto-growth settings, and available disk space.
This alert is raised based on the database metrics collection interval specified in Server Properties. For more information, see Set general server options.
When setting the thresholds for your Filegroup Space Full (Percent) alert, click Advanced > Autogrow Settings (see image below) and SQL Diagnostic Manager provides a choice for you to calculate your displayed percentage. Select Yes, alert on the current used size divided by the maximum possible size to take possible autogrowth into consideration when calculating the filegroup space full percentage. Select No, alert on the current used size divided by the current file size to calculate the filegroup space full percentage based only on the current size of the database disk file.