The cache file system (CacheFS) is a generic nonvolatile caching mechanism. CacheFS improves the performance of certain file systems by utilizing a small, fast local disk. For example, you can improve the performance of the NFS environment by using CacheFS.
CacheFS works differently with different versions of NFS. For example, if both the client and the back file system are running NFS version 2 or version 3, the files are cached in the front file system for access by the client. However, if both the client and the server are running NFS version 4, the functionality is as follows. When the client makes the initial request to access a file from a CacheFS file system, the request bypasses the front (or cached) file system and goes directly to the back file system. With NFS version 4, files are no longer cached in a front file system. All file access is provided by the back file system. Also, since no files are being cached in the front file system, CacheFS-specific mount options, which are meant to affect the front file system, are ignored. CacheFS-specific mount options do not apply to the back file system.
The first time you configure your system for NFS version 4, a warning appears on the console to indicate that caching is no longer performed.