Well, I have found out that cdrdao isn't always good at writing, sometimes cdrecord works where cdrdao doesn't. But that is offtopic here.

With readcd I have noticed this difference:

knoppix$ readcd -scanbus
scsibus0:
0,0,0 0) ' LG ' 'CD-ROM CRD-8322B' '1.02' Removable CD-ROM
0,1,0 1) *
0,2,0 2) *
0,3,0 3) *
...

while

knoppix$ cdrecord -scanbus
[...]
Linux sg driver version: 3.1.25
Using libscg version 'schily-0.8'.
scsibus0:
0,0,0 0) ' LG ' 'CD-ROM CRD-8322B' '1.02' Removable CD-ROM
0,1,0 1) 'HL-DT-ST' 'CD-RW GCE-8400B ' '1.02' Removable CD-ROM
0,2,0 2) *
0,3,0 3) *
...

I haven't tryed yet if I have the same problems with dhe first drive (which appears in the first list, unlike the second drive).