After more attempts and a few hours reading on this forum and the internet to get a share running with OMV I gave up.
It fascinates me that despite of a well defined hardware platform (Raspbian Pi Model B), a freshly downloaded installation file (OMV 2.0.15) and all the necessary steps I took following your video, it seems to be not possible to obtain a working share on a RPI.
Well, at least on my RPI.
So I decided to go back to basics, I am going to install Samba and of course I will have to read and study once again a lot of documentation.
Anyway, thanks again for your time and help!
Btw: I am very much willing to use and install again the OMV software, in case there is a newer and hopefully better version. Just let me know. Because the concept of the webbased interface with all its available options in OMV is still very attractive!