On Fri, Apr 3, 2009 at 8:20 PM, Wojtek <wojteko AT gmail DOT com> wrote:
> Let's say I configure a 2TB holding disk for amanda and I have 2
> projects. If that holding disk contains folders from both projects,
> will amanda know which one belongs to which before dumping?

If each project has a distinct directory name, then you will be able
to find the projects on the disk.

By the way, this is a very awkward use-case for Amanda, but one that
comes up fairly often.  The problem is that Amanda expects to make
daily "snapshots" of each DLE, and allow you to restore to one of
those snapshots.  In your case, Amanda also records the deletion of
projects after they have been dumped, meaning that a recovery requires
that you know the date on which that particular project was backed up.

It may make sense for the folks needing this use case to create a new
top-level Amanda utility that writes project directories to tape,
perhaps appending to tapes until they are full.  This would actually
be fairly easy, and all of the pieces you'd need are available from
Perl, or will be shortly.  In particular, there is a Perl class which
can handle writing to tape, including tape spanning, while reading
from a file descriptor.  This could pretty easily be hooked up to a
local GNU tar invocation to form a sort of cataloged, spanning,
error-tolerant, changer-wielding version of 'dd'.  If you play your
cards right, then amrestore can be used for recovery.

The hard part about this really lies in *designing* such a system.  If
you or anyone else using Amanda in this mode is interested in taking
this project on, a design discussion is the place to start.

If you want to see the shiny new code (which I'm pretty durn proud
of!), see device-src/xfer-dest-taper.c and perl/Amanda/Taper/Scribe.pm
in the last dozen or so commits to
  http://github.com/djmitche/amanda/tree/perltaper

> Also, what changes do I need to make to my config file so my
> incremental backups behave like real incremental, meaning if nothing
> changes, nothing is written to tape/holding disk.

If nothing changes, then Amanda writes *almost* nothing to the tape --
just a kilobyte or two, depending on the application.  This comes from
the "snapshot" model -- a "nothing changed" dump file is distinct from
a missing dump file (which might be confused with lost data).

Dustin

-- 
Open Source Storage Engineer
http://www.zmanda.com