The Art of SQL Server FILESTREAM - Red Gate Software

Chapter 2: Getting Started with FILESTREAMWhen SQL Server configures a file system folder as the FILESTREAM data container,it creates a file named filestream.hdr, and a folder named $FSLOG. Both of these filesystem objects are used by SQL Server internally and it is strongly recommended that youdo not access or modify them outside SQL Server.The filestream.hdr file stores the internal information that SQL Server uses to managethe BLOB data stored in the FILESTREAM data container, and to associate it with therelational data stored in the database tables. The $FSLOG folder is used to keep track ofthe changes applied on the BLOB data stored in the FILESTREAM data container, similarto a transaction log in a SQL Server database.It is important to remember that two databases cannot share the same file systemlocation to store their FILESTREAM data. It is not permitted even to use a subfolderwithin the FILESTREAM data container of one database to store the FILESTREAM datacontainer of another database.For example, assume that you have a FILESTREAM-enabled database named NorthPolewith a FILESTREAM data container located in C:\FS\NorthPole. Table 2-1 showssome examples of valid and invalid FILESTREAM data container locations for anotherFILESTREAM-enabled database called Southpole, assuming the NorthPole databasealready exists.FILESTREAM Data ContainerC:\FS\SouthPoleC:\FS\NorthPoleC:\FS\NorthPole\SouthPoleCommentsValidInvalid: C:\FS\NorthPole is already used by theSouthPole database.Invalid: C:\FS\NorthPole is already used by theNorthPole database; therefore the data containercannot be created as a subfolder.Table 2-1:Valid and invalid FILESTREAM data container locations.49