Effects of File and Disk Cache on Recoverability

The file cache is just an area of RAM that contains the data. When you write data to disk, Windows NT's lazy-write technique says that the data are written, when, in fact, they are still in RAM.

There can also be cache memory on the disk controller or on the disk itself. If you are running MS-DOS or Windows 3.1x, using the disk or controller caches can really help performance. The lazy-write technique in Windows NT improves performance to the point where you might not see much more improvement by using the cache on the disk or the controller.

This information should help you decide whether you want to enable the disk or controller cache:

• If disk performance is an issue, and specifically if the disk is being heavily written, turning on write caching is an option for improving performance, especially if it can be measured to improve the performance of the system.

• Controlling the write-back cache is a firmware function provided by the disk manufacturer. See the documentation supplied with the disk. You cannot configure the write cache from Windows NT.

• Write caching does not impact the reliability of the file system's own structures (metadata). NTFS instructs the disk device driver to insure that metadata writes get written through regardless of whether write caching is enabled or not. Non-metadata is written to the disk normally, so caching can occur for such data.

• Read caching in the disk has no impact on file system reliability.