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Matthias Bauer
bauerm (at) shoestringfoundation · org
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Tue, 08 Jul 2008

The ubiquitous fs in Plan9


The terms file server, file system and the abbreviation fs appear a lot in Plan9 documentation. For example, there are the manpages fs(3), fs(4), fs(8), and kfs(4).

First fs(4) aka Ken's FS. This was a file server inside the kernel which required a specially built kernel and was used together with a dedicated CPU server and many terminals. It is not part of the kernel sources any more, but its manpage lives on. To add confusion, there is also a manpage fs(8) for the console of Ken's fs.

Then there is kfs(4), a file system for terminals. It is implemented in user-space. No relation to Ken's FS besides the name. Strangely there seems to be no option to repair a broken kfs:

If the file system is inconsistent, the user is asked for permission to ream (q.v.) the disk.
(reaming means deleting). kfs cannot be managed by a console like Ken's fs and fossil, but by options to an executable kfscmd. UPDATE kfscmd has commands to repair a broken kfs.

As another example for the non-injectivity of abbreviations, there's fs(3) which is not a file system at all, but a kind of soft-raid that allows concatenation, striping and (simple) mirroring of files, e.g. disks.

On the fourth hand, there is fossil. This is the current default for CPU and File servers. It can be configured to move its blocks to an archival storage server venti. It is managed with its own console fossilcons which attaches itself not as /srv/fossilcons but /srv/fscons.

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