Sql Server FILESTREAM Total File Size

The following query will return the length in bytes of the filestreamcolumn column:

SELECT SUM(DATALENGTH(filestreamcolumn)) FROM filestreamtable;

Source

One disadvantage of Remus' solution is that it will not include the old versions of files that are available for garbage collection. They will no longer be part of logical database, but will still consume disk space until the Filestream garbage collector deletes them.

Starting with Sql Server 2008 R2, you can query the size column of sys.database_files for an approximate size (i.e. disk space used) of a given filestream container.