Good morning. I finally succeeded. What made the difference, I don't know.
Regarding the command I pasted above, there is one mistake: One should not address the partition (e.g. sdb1) but just the device (e.g. sdb). I tried both several times, so that is not the issue itself.
Though I did not need dvds in the end, I might buy me some for back-ups and future installations.
Thanks a lot for your time and help
