It worked!!! I have booted it right now
Thanks JohnB and gowater and others for being so helpful.

With 1m as bloksize, it took 2.8h to copy 20 gb.

I booted on the knoppix cd as I had no idea how I could
avoid having the primary drive mounted otherwise.

Would it have worked if the source drive was mounted while dd'ing it?

Thanks.
Best Regards from Denmark.