Re: [9fans] Anyone using p9p or Plan 9 venti as a more generic backup system?

[Bakul Shah <bakul+plan9@bitblocks.com>]

On Wed, 17 Nov 2010 09:44:27 PST David Leimbach <leimy2k@gmail.com>  wrote:
>
> On Wed, Nov 17, 2010 at 9:23 AM, dexen deVries <dexen.devries@gmail.com>wrote
> :
>
> > On Wednesday 17 November 2010 18:14:35 Venkatesh Srinivas wrote:
> > > (...)
> > > I'd be very careful with vac -m and -a on Unix; both have been at the
> > > root of considerable data-loss on a unix venti for me. I'd recommend
> > > vac-ing tarballs, rather than using vac's on unix trees directly. But
> > > your mileage may vary...
> >
> >
> > could you please elaborate a bit about that data loss?
> > traversing symlinks breaks? some files not getting read by vac at all?
> >
> > (I'm interested in using p9p vac+venti in similar manner, but on Linux w/
> > GNU stuff)
>
> I could imagine vac/unvac not dealing with resource forks or POSIX extended
> attributes and such properly, as well as potentially having difficulty with
> symlinks, but having dealt with stuff like that in "xar", I don't think it's
> too difficult to address.
>
> I may need to read up on venti and see what sorts of data types it supports.
>  Might be time to add some extensions?

venti doesn't care but vac/unvac do deal with symlinks, fifos
and special devices.  The problem with -a is that a
yyyy/mmdd/ prefix gets prepended to all paths and these dirs
are readonly (555). unvac coredumps in trying to extract
anything under yyyy/. The real problem is that unvac needs to
handle non-empty 555 dirs specially (like tar does).

Try this on unix:

mkdir -p a/b
chmod 555 a
tar cf - a | (cd /tmp; tar -xvf -)
vac a | (cd /tmp; unvac -v)

The basic problem is that venti & friends need some grunt work to
make them bullet/idiot proof.