Just to be sure, I took a new SD card, installed Xbian clean. this dmesg is after first boot:
fdisk, lsusb and dmesg
There is a lot more about USB.. but not sure if it will help me
Did one last test: RPi connected with its own (Blackberry) USB adapter, Harddisk via HUB to Pi. No change. Will search for a different hub..
Can you try connecting an usb stick to the usb hub? (To make sure the hdd itself isn't the problem)
Thanks for the tip. Eventually I figured out the issue. I even tried a HDD with its own power adapter and it didn't work. I tried an identical second hub and it didn't work (I bought 2).
Then I got the idea of replacing the A-B cable from hub to RPi with the one I use for a HDD with its own power. It worked!
So all that was wrong was a faulty A-B cable provided with one of the hubs and I kept using that one when I tested the second hub. The shop (modmypi) will send me a new A-B cable for free.
Thanks for the help!