File System Tiered Storage Filter Driver SDK, is a data storage technique which automatically moves data between high-cost and low-cost storage media. Tiered Storage Filter systems exist because high-speed storage devices, such as hard disk drive arrays, are more expensive (per byte stored) than slower devices, such as optical discs and magnetic tape drives. Tiered Storage Filter systems store the bulk of the enterprise's data on slower devices. A stub is created for and replaces each migrated file in the fast disk drives. On the local system, a stub file looks and act like a regular file. When you or a Windows application accesses a migrated file stub, the Windows operating system transparently directs a file access request to the Tiered Storage Filter driver. This driver retrieves the full file from the repository to which it was migrated.