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When re-using a rewritable DVD, I want to use the unused area of the disc.

So for example, when I burn a 1 GB Linux distro onto a rewritable DVD, and then burn other distro(s) onto the same DVD, it will use the same 1 GB area at the beginning of the DVD surface again and again. When the DVD no longer works, I will have used the 1 GB area at the start of the disc many times, and will have to 'throw away' the rest of the DVD, even though it is not used.

I am thinking that I could somehow modify the ISO, and add some dummy file at the beginning, which would never be read, and so the file possibly being bad / corrupted would not matter, since my actual files are on the fresh area of the DVD. Is this possible?

Photo of partially written DVD

Is there a way around this ?

2 Answers 2

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In principle, it is possible to modify an ISO by inserting a big enough dummy file. mkisofs even allows (via the -sort option) to put that dummy file at the beginning.

There are 2 problems remaining:

  • this dummy file might not be readable without errors if your DVD is worn out. That does not really matter, since that's what the dummy file is for.
  • some crucial information will always be located right at the beginning of the disk, so it will be overwritten every time. If a read error occurs there, you are out of luck.

Still: assuming that the disk degrades slowly, chances are that you can squeeze some more writes out of the disk.

Things to have a look at:

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  • Looks good, will certainly give it a go! Apr 1, 2015 at 8:48
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If you burn an ISO image, which expects a fixed order, there is probably no way to force use of the unused area, but if you are adding files, just put some dummy 1 GB files on before burning the rest. The dummy files should be large enough to occupy the used part; just leave them in place as you rewrite other files.

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  • Yep, I suppose I could do this (for normal data discs anyway), Is it possible to modify an ISO file, and force the 1GB 'dummy file' to be at the beginning of the ISO so that it gets burned in the right place ? Mar 4, 2015 at 15:55
  • You could change the ISO image by adding dummy files, but you would not achieve anything useful, since both the previously used and the unused sectors would be rewritten each time the ISO is updated. Mar 4, 2015 at 16:03
  • @JonasCz - The purpose of an iso file is to ensure the each bit is written to its proper location on the media. This is critical for content related to boot, and sometimes for hidden files that are used for purposes like licensing, etc. If the original is an iso rather than something like an archive file or collection of files in a folder, it is probably because it needs to remain an unaltered disk image.
    – fixer1234
    Mar 4, 2015 at 18:00
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    @JonasCz I messed around with ISO files a long time ago and I found out (from a forum, I don't remember which it was) that if you used a hex editor to append bytes to an ISO image and then burn it to disc, your modifications would be burnt to the disc but wouldn't show up in the file manager. The only way to access the 'hidden' data again would be to make an image of the disc and use a hex editor to retrieve the bytes in the end, possibly looking for a byte pattern or 'marker'. Maybe this could be applied to beginning of the ISO file as well?
    – Vinayak
    Mar 27, 2015 at 8:38
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    @JonasCz How about using multisession to achieve what you want? You could burn a non-bootable ISO with a file that's big enough to occupy the area of the DVD that you wish to ignore, close the session but you don't finalize the disc. Then you burn another session with bootable ISO and opt to not preserve the data from the previous session. I haven't tried this of course, but someone might have. Some more info here: puppylinux.com/multi-puppy.htm
    – Vinayak
    Mar 27, 2015 at 11:02

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