Windows NT cnss file system driver

The Native Structured Storage (NSS) implementation within OLE Structured Storage was available but later the CNSS.SYS filter was removed from the Windows 2000. Would be interesting to implement that in ReactOS.

Another service that uses reparse points is the Native Structured Storage (NSS) service. The NSS file system filter makes a file on the disk look like an OLE-structured storage file. An OLE document may contain data for a Word document, a spreadsheet, a PowerPoint presentation, and so on. Historically, the OLE libraries have placed all of the data for these different embedded "objects" in a single file. This makes it very easy to copy a file from one place to another and take all of the embedded objects with it. But if you modify any of these objects, the updated objects are placed at the end of the file, and the old objects are not removed from the file. The old objects were not removed to improve performance; if OLE removed these objects, it would have to rewrite the entire file to disk, taking up a lot of time. OLE document files are consequently much larger than they need to be and waste a lot of disk space.
By taking advantage of NTFS 5.0 with its support for streams, reparse points, and NSS, OLE documents no longer waste precious disk clusters and do not have a performance penalty. Each of the embedded object's data now resides in its own stream within a file. Updating an object means that a new stream is created for the new object and that the original stream for the object is destroyed, causing the file system to reclaim the disk space. The NSS file system filter makes all of this appear transparent to an application. The NSS filter also allows an NSS file to be copied to a floppy, converting the file to the old file format and vice versa.