FILESTREAM is a new datatype in SQL SERVER 2008. To use FILESTREAM, a database needs to contain a FILESTREAM filegroup and a table which contains a varbinary(max) column with the FILESTREAM attribute set. This causes the Database Engine to store all data for that column in the file system, but not in the database file. A FILESTREAM filegroup is a special folder that contains file system directories known as data containers. These data containers are the interface between Database Engine storage and file system storage through which files in these data containers are maintained by Database Engine.
Keynotes about FileStream data type: