This metric calculates the percentage of the allocated disk space for databases that is being used by the SQL Server instance. The total size allocated to the databases is the sum of unused space, data space, and index space. Data space includes leaf level clustered index pages, since these pages are the data pages. Index space excludes the leaf pages of clustered indexes. The Files view on the Databases tab allows you to view detailed data file information including the data size and the percentage of allocated file size being used on each of your databases.