[Discuss] Versioning File Systems

[Shankar Viswanathan]

On Thu, May 3, 2012 at 2:33 PM, Richard Pieri <richard.pieri at gmail.com> wrote:
> Snapshots aren't at all close to versioning.  A versioning file system keeps
> (or can keep; one can usually configure how many versions to keep) every
> version of a file saved.  File system snapshots get the file system state
> when the snapshots are made.
>
> For example: create a ZFS snapshot.  Create a file.  Edit it and save it.
>  Repeat nine more times.  Create another snapshot.  How many versions of the
> file do you have?  You would have just one on ZFS.  You would have all
> eleven on a versioning file system.

Talking about versioning filesystems, why haven't they been popular on
Unix/Linux? I know RSX-11 and VMS implemented versioning filesystems
which were used quite extensively in development environments. I am
aware of VFS implementations for Linux such as ext3cow and NILFS but
haven't actually seen them used anywhere. I have always wondered why
we don't see more uses of this idea.

I know ClearCase implements a virtual filesystem to create a "view" of
the versioned object, but I don't believe the versioning is handled
natively in the filesystem -- the versioning I think is handled by a
separate database.

-Shankar