Fossil (file system)
Encyclopedia
Fossil is the default file system
in Plan 9 from Bell Labs
. It serves the network protocol 9P
and runs as a user space
daemon
, like most Plan 9 file servers. Fossil is different from most other file systems due to its snapshot
/archival feature. It can take snapshots of the entire file system on command or automatically (at a user-set interval). These snapshots can be kept on the Fossil partition as long as disk space allows; if the partition fills up then old snapshots will be removed to free up disk space. A snapshot can also be saved permanently to Venti
. Fossil and Venti are typically installed together.
To access a snapshot, one would connect to a running fossil instance (“mount” it) and change directory to the desired snapshot, e.g. /snapshot/yyyy/mmdd/hhmm (with yyyy, mm, dd, hh, mm meaning year, month, day, hour, minute). To access an archive (permanent snapshot), a directory
of the form /archive/yyyy/mmdds (with yyyy, mm, dd, s meaning year, month, day, sequence number) would be used. Plan 9 allows modifying the namespace
in advanced ways, like redirecting one path to another path (e.g. /bin/ls to /archive/2005/1012/bin/ls). This significantly eases working with old versions of files.
and added to the Plan 9 distribution at the end of 2002. It became the default file system in 2003, replacing Kfs
and the previous Plan 9 archival file system, dubbed The Plan 9 File Server, or "fs". fs is also an archival file system which originally was designed to store data on a WORM
optical disc system. The permanent storage for fossil is provided by Venti
, which typically stores data on hard drives, which have much lower access times than optical discs.
File system
A file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
in Plan 9 from Bell Labs
Plan 9 from Bell Labs
Plan 9 from Bell Labs is a distributed operating system. It was developed primarily for research purposes as the successor to Unix by the Computing Sciences Research Center at Bell Labs between the mid-1980s and 2002...
. It serves the network protocol 9P
9P
9P is a network protocol developed for the Plan 9 from Bell Labs distributed operating system as the means of connecting the components of a Plan 9 system. Files are key objects in Plan 9. They represent windows, network connections, processes, and almost anything else available in the operating...
and runs as a user space
User space
A conventional computer operating system usually segregates virtual memory into kernel space and user space. Kernel space is strictly reserved for running the kernel, kernel extensions, and most device drivers...
daemon
Daemon (computer software)
In Unix and other multitasking computer operating systems, a daemon is a computer program that runs as a background process, rather than being under the direct control of an interactive user...
, like most Plan 9 file servers. Fossil is different from most other file systems due to its snapshot
Snapshot (computer storage)
In computer systems, a snapshot is the state of a system at a particular point in time. The term was coined as an analogy to that in photography. It can refer to an actual copy of the state of a system or to a capability provided by certain systems....
/archival feature. It can take snapshots of the entire file system on command or automatically (at a user-set interval). These snapshots can be kept on the Fossil partition as long as disk space allows; if the partition fills up then old snapshots will be removed to free up disk space. A snapshot can also be saved permanently to Venti
Venti
Venti is a network storage system that permanently stores data blocks. A 160-bit SHA-1 hash of the data acts as the address of the data...
. Fossil and Venti are typically installed together.
Features
Important features include:- Snapshots are available to all users. No administrator intervention is needed to access old data. (This is possible because Fossil enforces file permissions; users can only access data which they would be allowed to access anyway; thus a user cannot snoop on another's old files or look at old passwords or such.)
- Data in permanent snapshots (sometimes called archives) cannot be modified. Only the non-permanent snapshots can be removed.
To access a snapshot, one would connect to a running fossil instance (“mount” it) and change directory to the desired snapshot, e.g. /snapshot/yyyy/mmdd/hhmm (with yyyy, mm, dd, hh, mm meaning year, month, day, hour, minute). To access an archive (permanent snapshot), a directory
Directory (file systems)
In computing, a folder, directory, catalog, or drawer, is a virtual container originally derived from an earlier Object-oriented programming concept by the same name within a digital file system, in which groups of computer files and other folders can be kept and organized.A typical file system may...
of the form /archive/yyyy/mmdds (with yyyy, mm, dd, s meaning year, month, day, sequence number) would be used. Plan 9 allows modifying the namespace
Namespace (computer science)
A namespace is an abstract container or environment created to hold a logical grouping of unique identifiers or symbols . An identifier defined in a namespace is associated only with that namespace. The same identifier can be independently defined in multiple namespaces...
in advanced ways, like redirecting one path to another path (e.g. /bin/ls to /archive/2005/1012/bin/ls). This significantly eases working with old versions of files.
History
Fossil was designed and implemented by Sean Quinlan, Jim McKie and Russ Cox at Bell LabsBell Labs
Bell Laboratories is the research and development subsidiary of the French-owned Alcatel-Lucent and previously of the American Telephone & Telegraph Company , half-owned through its Western Electric manufacturing subsidiary.Bell Laboratories operates its...
and added to the Plan 9 distribution at the end of 2002. It became the default file system in 2003, replacing Kfs
KFS
KFS may refer to*Kuali Financial Systems*Korean Fiber Society*Koç Financial Services*CloudStore, previously known as Kosmosfs*Kristeligt Forbund for Studerende*King Features Syndicate...
and the previous Plan 9 archival file system, dubbed The Plan 9 File Server, or "fs". fs is also an archival file system which originally was designed to store data on a WORM
Write Once Read Many
A Write Once Read Many or WORM drive is a data storage device where information, once written, cannot be modified. On ordinary data storage devices, the number of times data can be modified is not limited, except by the rated lifespan of the device, as modification involves physical changes that...
optical disc system. The permanent storage for fossil is provided by Venti
Venti
Venti is a network storage system that permanently stores data blocks. A 160-bit SHA-1 hash of the data acts as the address of the data...
, which typically stores data on hard drives, which have much lower access times than optical discs.
External links
- Fossil manual page
- Fossil console commands manual page
- Technical fossil paper, about data structures written to venti