Re: [RFC 12/26] ext2 white-out support

[Jan Blunck <jblunck@suse.de>]

On Wed, Aug 01, Erez Zadok wrote:

> There are three other reasons why Unionfs and our users like to have
> multiple writable branches:
> 

...

>    And yes, it does make our implementation more complex.

And error-prone and unflexible wrt to changes. When XIP was introduced,
unionfs crashed all over this changes. I don't know if this has changed
yet. Not speaking of other issues like calling back into VFS (stack usage),
locking problems and so on.

> 3. Some people use Unionfs in the scenario described in point #2 above, as a
>    poor man's space- and load- distribution system.  Some of our users like
>    the idea of controlling how much storage space they give each branch, and
>    how much it might grow, and even how much CPU or I/O load might be placed
>    on each of the lower filesystems which serve a given branch.  That way
>    they worry less about the top-layer's space filling up more quickly than
>    expected.  Now Unionfs was never designed to be a load-balancing f/s (we
>    have RAIF for that, see <http://www.filesystems.org/project-raif.html>),
>    but users seems to always find creative ways to [ab]use one's software in
>    ways one never thought of. :-)

And this has nothing to do with unioning ...

> BTW, does Union Mounts copyup on meta-data changes (e.g., chmod, chgrp,
> etc.)?

No. But it was proposed during on of the last postings.