Date:	Tue, 9 Jan 2007 20:03:15 +0200
From:	"Raz Ben-Jehuda(caro)" <raziebe@...il.com>
To:	"Erez Zadok" <ezk@...sunysb.edu>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/24] Unionfs: Documentation

On 1/9/07, Erez Zadok <ezk@...sunysb.edu> wrote:
> In message <20070109095345.GB12406@...radead.org>, Christoph Hellwig writes:
> > On Mon, Jan 08, 2007 at 07:03:35PM -0500, Erez Zadok wrote:
> > > However, I must caution that a file system like ecryptfs is very different
> > > from Unionfs, the latter being a fan-out file system---and both have very
> > > different goals.  The common code between the two file systems, at this
> > > stage, is not much (and we've already extracted some of it into the "stackfs
> > > layer").
> >
> > I think that's an very important point.  We have a chance to get that
> > non-fanout filesystems right quite easily - something I wished that would
> > have been done before the ecryptfs merge - while getting fan-out stackable
> > filesystems is a really hard task.  In addition to that I know exactly
> > one fan-out stackable filesystem that is posisbly useful, which is unionfs.
>
> Christoph, on our Unionfs mailing list, we've been asked numerous times for
> additional functionality.  People asked for load balancing based on CPU
> time, rtt, latency, space available, etc.  People asked for replication
> functionality.  People asked for failover.  And more.  Some users have
> become so motivated, that they developed and maintain their own Unionfs
> patches to support rudimentary load-balancing and replication.
>
> Our answer had always been the same: those features are nice, but have no
> place in Unionfs.  That's why we've created RAIF, exactly to give all those

Erez hello
my name is raz.
Just for my better understanding , raifs stands for raided file system ?
what sort of raids do they have ?
thank you
raz




> who wanted "just one more thing added to Unionfs" another f/s to play with.
> Who knows, maybe one day, some of those features may wind up in a Unionfs-NG
> or as composable VFS plugins.  But for now, we've given the community RAIF
> so they can play with it, experiment, enhance, whatever.  RAIF is newer
> than Unionfs and for now we're just accumulating experience with it.
>
> In other words, I think there are other fan-out file systems of use other
> than Unionfs.  If and when Unionfs made it into mainline, I'll guarantee you
> that you'll have users asking for other fan-out functionality.  That is why I
> think it is prudent to wait and gather more experience with stackable file
> systems in Linux, before embarking on a more generic functionality layer,
> which would support non-fanout as well as fanout extensions.
>
> > Because of that I'm much more inclined to add VFS asistance for this
> > particular problem (unioning) instead of adding complex infrastructure
> > to solve a general problem that people don't benefit from.
>
> I'd love to see VFS assistance for Unioning in particular and for stacking
> in general.  But again, I prefer to gather some practical experience first,
> and then try to generalize any new VFS-level helper functionality.
>
> Sincerely,
> Erez.
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-- 
Raz
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