If you try to edit a file on a newer FreeNAS you may get a error message about it being a read-only filesystem. Most of the time, this is not a problem since FreeNAS is designed around having most of the system mounted a read-only. However, if you are trying to update the ~/.cshrc file, you'll run into a need to remount the file system read-write.
mount -o noatime -uw /
mount -o noatime -ur /