I issued:

growisofs -Z /dev/dvd=/dev/zero

there it goes:

Executing 'builtin_dd if=/dev/zero of=/dev/dvd obs=32k seek=0'
11665408/4700372992 ( 0.2%) @2.5x, remaining 46:53
23298048/4700372992 ( 0.5%) @2.5x, remaining 33:27
**** **** ****
**** **** ****
**** **** ****
**** **** ****
4697751552/4700372992 (99.9%) @2.5x, remaining 0:00

(And then it pulls one of these on me.... look below)

:-[ LBA=230540h, SENSE KEY=5h/ASC=21h/ASCQ=00h ]
:-( write failed: Invalid argument
/dev/dvd: flushing cache
/dev/dvd: stopping de-icing
/dev/dvd: writing lead-out
/dev/dvd: reloading tray


Does anyone have an idea what this LBA=230540h, SENSE KEY=5h/ASC=21h/ASCQ=00h may exactly mean?

IIRC, cdrecorder used to give a similar error when it came to the end of a disc if a file of indefinite size was supplied. I'm fairly sure it's harmless in your case, but you can supply the mkisofs option -stream-media-size to growisofs prevent it.