If both the CacheFS client and the CacheFS server are running 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.
If you want to implement your CacheFS mounts as in previous Solaris releases, then specify NFS version 3 in your CacheFS mount commands. For example:
mount -F cachefs -o backfstype=nfs,cachedir=/local/mycache,vers=3 starbug:/docs /docs