CacheFS is the name used for several similar software technologies designed to speed up

distributed file system A clustered file system is a file system which is shared by being simultaneously mounted on multiple servers. There are several approaches to clustering, most of which do not employ a clustered file system (only direct attached storage for ...

file access for networked computers. These technologies operate by storing ( cached) copies of files on secondary memory, typically a local

hard disk A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with mag ...

, so that if a file is accessed again, it can be done locally at much higher speeds than networks typically allow. CacheFS software is used on several

Unix-like A Unix-like (sometimes referred to as UN*X or *nix) operating system is one that behaves in a manner similar to a Unix system, although not necessarily conforming to or being certified to any version of the Single UNIX Specification. A Unix-li ...

operating systems. The original Unix version was developed by

Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, ...

in 1993. Another version was written for Linux and released in 2003. Network filesystems are dependent on a

network Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematics ...

link and a remote

server Server may refer to: Computing *Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients Role * Waiting staff, those who work at a restaurant or a bar attending customers and su ...

; obtaining a file from such a

filesystem In computing, file system or filesystem (often abbreviated to fs) is a method and data structure that the operating system uses to control how data is stored and retrieved. Without a file system, data placed in a storage medium would be one larg ...

can be significantly slower than getting the file locally. For this reason, it can be desirable to cache data from these filesystems on a local disk, thus potentially speeding up future accesses to that data by avoiding the need to go to the network and fetch it again. The software has to check that the remote file has not changed since it was cached, but this is much faster than reading the whole file again.

Prior art

Sprite (operating system) Sprite is an experimental Unix-like distributed operating system developed at the University of California, Berkeley by John Ousterhout's research group between 1984 and 1992. Its notable features include support for single system image on compute ...

used large disk block caches. These were located in main-memory to achieve high performance in its file system. The term CacheFS has found little or no use to describe caches in main memory.

Grossmont version

The first CacheFS implementation, in 6502 assembler, was a write through cache developed by Mathew R Mathews at Grossmont College. It was used from Fall 1986 to Spring 1990 on three diskless 64 kB main memory Apple IIe computers to cache files from a Nestar file server onto Big Board, a 1 MB DRAM secondary memory device partitioned into CacheFS and TmpFS. The computers ran Pineapple DOS, an Apple DOS 3.3 derivative developed in the course of a follow on to WR Bornhorst's NSF funded Instructional Computing System. Pineapple DOS features, including caching, were unnamed; the name CacheFS was introduced seven years later by Sun Microsystems.

Sun version

The first Unix CacheFS implementation was developed by

and released in the Solaris 2.3 operating system release in 1993, as part of an expanded feature set for the NFS or Network File System suite known as Open Network Computing Plus (ONC+).New Features in Solaris 2.4
in the Solaris 2.4 AnswerBook documentation, Sun Microsystems, 1994. Accessed Sept 10, 2007 It was subsequently used in other UNIX operating systems such as

Irix IRIX ( ) is a discontinued operating system developed by Silicon Graphics (SGI) to run on the company's proprietary MIPS workstations and servers. It is based on UNIX System V with BSD extensions. In IRIX, SGI originated the XFS file system ...

(starting with the 5.3 release in 1994). IRIX 6.5 ONC3/NFS Administrators Guide
, Silicon Graphics, 2005. Accessed Sept 10, 2007
{{Webarchive, url=https://web.archive.org/web/20071019203914/http://ryan.tliquest.net/sgi/irix_versions.html#I5 , date=2007-10-19 , Ryan Thoryk, revision of January 18, 2007. Accessed Sept 10, 2007

Linux version

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which i ...

operating systems now commonly use a new version of CacheFS developed by David Howells. Howells appears to have rewritten CacheFS from scratch, not using Sun's original code. The Linux CacheFS currently is designed to operate on

Andrew File System The Andrew File System (AFS) is a distributed file system which uses a set of trusted servers to present a homogeneous, location-transparent file name space to all the client workstations. It was developed by Carnegie Mellon University as part of t ...

and

Network File System Network File System (NFS) is a distributed file system protocol originally developed by Sun Microsystems (Sun) in 1984, allowing a user on a client computer to access files over a computer network much like local storage is accessed. NFS, li ...

filesystems.

Terminology

Because of its similar naming to FS-Cache, CacheFS'

terminology Terminology is a group of specialized words and respective meanings in a particular field, and also the study of such terms and their use; the latter meaning is also known as terminology science. A ''term'' is a word, compound word, or multi-wo ...

is confusing to outsiders. CacheFS is a backend for FS-Cache and handles the actual data storage and retrieval. FS-Cache passes the requests from netfs to CacheFS.

FS-Cache

The cache facility/layer between the cache backends just like CacheFS and NFS or AFS.

Cache backends

CacheFS

CacheFS is a Filesystem for the FS-Cache facility. A

block device In Unix-like operating systems, a device file or special file is an interface to a device driver that appears in a file system as if it were an ordinary file. There are also special files in DOS, OS/2, and Windows. These special files allow ...

can be used as cache by simply mounting it. Needs no special activation and is deactivated by unmounting it.

Cachefiles (daemon)

Daemon Daimon or Daemon (Ancient Greek: , "god", "godlike", "power", "fate") originally referred to a lesser deity or guiding spirit such as the daimons of ancient Greek religion and mythology and of later Hellenistic religion and philosophy. The wo ...

using an existing filesystem (

ext3 ext3, or third extended filesystem, is a journaled file system that is commonly used by the Linux kernel. It used to be the default file system for many popular Linux distributions. Stephen Tweedie first revealed that he was working on exten ...

with user_xattr) as cache. Cache is bound with "cachefilesd -s".

Project status

Project status seems to be stalled, and some people are attempting to revive the code and bring it up to date.Gilliam, Paul

"linux-cachefs mailing list", September 29, 2010

Features

The facility can be conceptualised by the following

diagram A diagram is a symbolic representation of information using visualization techniques. Diagrams have been used since prehistoric times on walls of caves, but became more prevalent during the Enlightenment. Sometimes, the technique uses a three ...

: The facility (known as FS-Cache) is designed to be as transparent as possible to a user of the system. Applications should just be able to use NFS files as normal, without any knowledge of there being a cache.

References

External links

Fscache-ols2006 PresentationD.Howells@Red Hat

Steve D.@Red HatRed Hat CacheFS mailinglist
Outdated articles?
LWN.NET
A general caching filesystem
LWN.NET
Initial mail introducing cacheFS for Linux Network file systems