Our SQL Server 2014 server is running on Windows Server 2012 R2. The drive space properties reported by the OS shows that we had 17 GB free one day, and the next day it shows we have only 718 MB free. No particular queries nor SQL Jobs were ran during this time. The database maxsize is set to Unlimited (growth is set to 10%), and executing this query:
SELECT ( SELECT SUM(CAST(df.size AS FLOAT)) FROM sys.database_files AS df WHERE df.type IN (0, 2, 4) ) AS [DbSize], SUM(a.total_pages) AS [SpaceUsed], ( SELECT SUM(CAST(df.size AS FLOAT)) FROM sys.database_files AS df WHERE df.type IN (1, 3) ) AS [LogSize] FROM sys.partitions p JOIN sys.allocation_units a ON p.partition_id = a.container_id LEFT JOIN sys.internal_tables it ON p.object_id = it.object_id
...to get the DB size vs space used, shows we are actually 12 GB below the current database size.
So is it possible that Windows suddenly updated the reported space available, taking into account the unused portion of space?