However, I did not fully understand how I should burn it directly (I tried to use both mkisofs-cdrecord and kb3 - unsuccessfully). Do you mean that I can do it just through cdrecord? Still my problem is more complicated, as my tarball is much larger than 4GB and splitted it in 3 pieces. Well, I know that a clear workaround would be to split it in, say, 6 pieces and make every ISO out of every two of them, but that would be too easy would not it?
The suggestion was to write your data directly to the media, just like you would do with a tape, rather than formatting it as an ISO filesystem. So you don't make an ISO, and hence don't need mkisofs.
Paul.