[openbeosstorage] Re: ISO9660/cdrom progress
- From: Tyler Dauwalder <tyler@xxxxxxxxxxxxx>
- To: openbeosstorage@xxxxxxxxxxxxx
- Date: Sun, 16 Feb 2003 00:14:35 -0800
> > "Ingo Weinhold" <bonefish@xxxxxxxxxxxxxxx> wrote:
> [...]
> > > > But that's not enough - we don't support them correctly, we
> > > > always
> > > > have
> > > > to export all sessions, but there should be a way to
> > > > differentiate
> > > > multi-session sessions from others, so that Tracker only shows
> > > > the
> > > > last
> > > > sessions, without having to care about it.
> > > > But you should always be able to mount every single session from
> > > > the
> > > > shell as it was (perhaps even from within Tracker, perhaps with
> > > > a
> > > > submenu for a session=3D3F - although that would require extra
> > > > coding,
> > > > it
> > > > might be a nice solution for power-users).
> > > But isn't that a feature that should be into the Tracker rather
> > > than
> > > into some API=3F I mean, the device API provides all information
> > > available. If the user wishes -- or let it be the default behavior
> > > --
> > >
> > > that only the last sessions of a multi-session CD should be
> > > available,
> > > than this is something the Tracker can provide easily. Or do I
> > > miss
> > > something=3F
> >
> > Perhaps :) Tracker need to have an understanding about which
> > sessions
> > make up a multi-session volume, or else it can't offer that feature
> > to
> > the user.
> > Now, only the session add-on itself know which session is part of a
> > multi-session volume, and which is not. It has to make that
> > information
> > available in some way.
>
> Er, I probably just don't know about multi-session CDs. A CD doesn't
> simply consist of sessions, but these sessions are grouped in
> volumes??
> If that is so, it should be an information the Disk Device API is able
> to provide.
With iso9660 file systems, you can refer to file data from previous
sessions instead of duplicating the same data over again. So, say you
have 20 files that you back up on a CD. Then a week later, you want to
back them up again, but only one of them has changed. Instead of
writing all 20 files again, only the changed file will be written, and
the remaining entries will just refer to the data in the previous
session.
So, I think that it's not really a session add-on thing as much as a
file system add-on thing. With iso9660, I believe all the related
volumes have a common "volume set" identifier (I'd need to double check
this, though). We'd probably need something similar to be able to
distinquish which volumes are part of a set and which volumes are
independent. We'd probably also need a way to designate the
chronological ordering of the volumes; either a datestamp or an
ordinal numbering, I suppose. I'm nearly done revamping the session
module, so I could look into the details of how iso9960 handles things
after I finish. Thoughts?
-Tyler
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