I did sort it out different though:
I moved some stuff in the /var/hda directory around and changed the mount point of the logical volume from /var/hda/files to /var/hda. then I copied some stuff back and it worked.
anyway, with everything sorted alright I set out to do some backups, and that worked great, BUT...
during the backup process I heard a lot of clicking noises from my drive (got it last tuesday)... so I ran smartctl (SMART monitoring tool for disks) and after that the Seagate linux cli-tool, during which I received a very nice I/O error and lots of clickies and an unresponsive server... the drive is DOA


I'm going to RMA it tomorrow, luckily I've also ordered a 1TB disk which should come in tomorrow (it was on sale, I couldn't resist for that kind of money), so I'll probably be up and running again soon.
When I get my RMA'd drive/replacement I can do my thingy and extend my VG & LV as planned, and I'll have a nice 1,5TB storage available...