[linux-elitists] Cluster filesystems

Martin Pool mbp@sourcefrog.net
Sat Jan 3 19:26:29 PST 2004


On  1 Jan 2004, Jason Spence <jspence@lightconsulting.com> wrote:

>  - Is there a UNIX style solution to the simultaneous update problem?
>    All the current non sucky solutions I've seen involve either
>    preventing writes during disconnected operation or changing the
>    file abstraction in some way, whether it be involving the
>    filesystem with counting lines in the file or doing a VMS style
>    record scheme.  Both strike me as kind of counter to the
>    traditional way of doing things in UNIX...

Unison <http://www.cis.upenn.edu/~bcpierce/unison/> is very good for this.

It is not a distributed filesystem, but rather a tool for
resynchronizing two-way updates to intermittently connected replicas.
The typical use is keeping a working directory on both your laptop and
desktop.

Doing it in a separate userspace app rather than the filesystem is
arguably more Unixy, and certainly more portable, though you lose some
features like pooled storage and continuous synchronization.

Essentially you keep copies of the directory on two machines, and
resynchronize when you wish.  If a single file has been changed on two
machines, you need to reconcile those changes by some external means.

-- 
Martin



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