About file system filter drivers

File system filter drivers on Windows

A file system filter driver is an optional driver that adds value to or modifies the behavior of a file system. It is a kernel-mode component that runs as part of the Windows executive.

A file system filter driver can filter I/O operations for one or more file systems or file system volumes. Depending on the nature of the driver, filter can mean log, observe, modify, or even prevent. Typical applications for file system filter drivers include antivirus utilities, encryption programs, and hierarchical storage management systems.

There are two file system filter models in Windows:

Note

For optimal reliability and performance, use file system minifilter drivers with Filter Manager support instead of legacy file system filter drivers. To port your legacy driver to a minifilter driver, see Guidelines for Porting Legacy Filter Drivers.

File system filter drivers are not device drivers

A device driver is a software component that controls a particular hardware I/O device. For example, a DVD storage driver controls a DVD drive.

In contrast, a file system filter driver works in conjunction with one or more file systems to manage file I/O operations. These operations include:

  • Creating, opening, closing, and enumerating files and directories

  • Getting and setting file, directory, and volume information

  • Reading and writing file data

In addition, file system filter drivers must support file system-specific features such as caching, locking, sparse files, disk quotas, compression, security, recoverability, reparse points, and volume mount points.

For more details on the similarities and differences between file system filter drivers and device drivers, see the following: