Thank you Budy,
Well this seemed a bit odd, but that helped. Since I'm still benchmarking, I don't have replication setup, nor mirroring, nor backup.
Actually deleting the volume is something I was able to do(after a reboot), but deleting the a volume group - that is something I cannot manage to.
According to Todd, DSS6 will ship in early July, but as always, don't rely too much on that. The release date of Atlanta, a special version of DSS5, had been posponed a couple of times, making it from January to April, if I rememer correctly.