Backup on DVD-RW: ISO 9660 file system overhead

[Simon Jolle sjolle <urandomdev@gmail.com>]

Hi Debian Users

I am doing a backup of Thunderbird mails. As u can see the Space on disk 
is 400 MB less than the space on ISO image.

How can I avoid that much wasted space?

$ du -sh .mozilla-thunderbird/; du -sh mail_archive_20jun08.iso
1.8G	.mozilla-thunderbird/
2.2G	mail_archive_20jun08.iso

I did the following command:

$ mkisofs -J -r -o mail_archive_20jun08.iso
/home/sjolle/.mozilla-thunderbird/

Did I use the wrong options?

cheers
Simon

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