[Debburn-devel] Do you know a good dvd burner emulator

[Thomas Schmitt]

Hi,

> > The 2x Verbatims live since 2004.
> But how many times you usually record them a day?

Currently two of them serve in incremental backups.
They get added a session about every fourth day.
One took 43 sessions as sequential DVD-RW and now
serves a second turn as formatted DVD-RW having
12 (pseudo-)sessions meanwhile.
I would assume that i did not use it more than
50 times before. Mostly in formatted state, but
also sequential (after 40 minutes of blanking).


> I like linux-kernel code style, and your project is exactly what I like.

Somehow libburn seems to stem from kernel code.
I am not sure because i'm not its founder and
we took over without the consent of the founders.


> isn't there a limit (99) on track count?

On CD media, yes. 
Worse: you cannot write 99 sessions because there
are gaps of more than 10 MB after each session.

With DVD-R the gaps are about 8 MB and you can
write lots of sessions.
With DVD+R the gap is 4 MB but you can write only
153 (or 254 ?) sessions.
(see MMC-5 4.3.6.2.2 for numbers 153 and FFh)


> I would rather open a track, and write it in chunks (packets), and use
> variable size packets, and close it when disk is unmounted.

On CD-R[W] this might work.

On DVD-R[W] you are restricted to a multiple of 32 KiB
blocks. This applies to both, formatted and unformatted.
Same with DVD+R.
With DVD+RW you suffer a performance penalty if not
aligned to 32 KiB.
The natural block size for BD-R[E] is 64 KiB.

But there is the restriction that you are not supposed
to read during writing a session on sequential media.
(MMC-5 6.44.3.3 SAO Raw on CD-R/-RW, DAO and Incremental
 on DVD-R/-RW)
Whether the consequences are tolerable with packet
write modes has still to be tested.
Currently libburn refuses to read while a write
session is going on.


> session probably needs to be closed to, but I think I can leave it open, and
> close it when user explicitly asks for that.

That would be the suspicious -nofix option of
wodim and cdrecord.


> (I once had HP CD burner, and it worked that way, it closed session when an
> option "convert disk
> so it can be read in ordinary CD" was selected.

Are you sure it closed the session and not the disc ?
(I.e. not -multi rather than not -nofix.)
I read rumors that appendable media might not be
readable in some CD players.

All in all i would frown on ejecting a media with
an open session (if the drive is willing to obey
at all).

But as long as the media stays loaded, that long
it should be possible to keep open a session on
all media except fast blanked DVD-RW.
This session should be allowed to be written
sequentially with arbitrary idle times inbetween.


> So for now no more questions, Thanks,

Give me a note when you begin to feel ready for
CD packet writing and/or formatting experiments.
I will probably need a week from then on to
make a first test version of libburn for that.

The DVD stuff should already be prepared for
experiments if you use  
  burn_write_opts_set_write_type(
     opts, BURN_WRITE_TAO, BURN_BLOCK_MODE1);
and provide a burn_source object which puts out
some 32 KiB blocks from time to time.

The most interesting experiment to be made is
whether you may read data while writing in
packet mode to sequential media. For that
i will have to lift the read ban in libburn.

If not then you will have to cache your writes
until they are large enough to be written as
a session.
I would expect problems at least with CD-R
and DVD-R.


Have a nice day :)

Thomas