Thanks a lot Dima!
VBB is already working perfectly in the (I suppose) supported environment (Windows VM on ESX with passthrough SCSI controller + tape library).
That said, we're still talking of a small home setup (backup of personal data that I store in big quantities as a hobbyist photographer) so whether the solution is supported or not, it's not a real issue for me. But as a geek and +20 year IT professional, I was trying to hack my way around adaptec's faulty driver's limitations.
B plans being:
- the LSI 20320 controller I just bought for 15€ (its driver will allow me to set a block size up to 2MB)
- starwind's stand-alone tape director (if they are able to send me an old 32 bit version which existed but can't be found anywhere on the internet)
- correct iSCSI target setup in linux with TGT (looks like the tape drive is getting continuously disconnect so there more chances that the (wrong) iSCSI setup is causing VBB not to see the changer rather than VBB having a problem itself.
I will try to come back with my findings to share with the community