Ok, after some more investigations it seems that my data is gone... still not sure what was the reason, but I would like to understand if I make a mistake and how to behave in such a situation...
So here are the steps what I have done:
1. I update my freenas to the latest version U3
2. Reboot after that was successful
3. I recognized that boot environment is still on U2 - so I switched the boot environemnt to latest U3
4. System have not booted any more (Grub Rescue Mode)
5. As I was not able to boot, I installed a new freenas U3 installation on an new usb stick (the old ones are still in the system) and I have booted from the new stick
6. During boot an automatic "zpool import" was started. Here it seems to have a problem because booting stops and console ends with a "db>" shell (as I remember)
7. After new reboot system booted and my data zpool array and server configuration was available, but no data was existing any longer (see screenshots earlier provided)
zpool status shows "Healthy" for my Data pool - but as no data in in here it won't help me.
My unstanding was that the data zpool is independant from any boot issues so that even if there is a boot problem the data partiations could not have any problems...
I am not sure what exactly went wrong here, so maybe someone can help me avoiding such a problem once it comes again in the future... of course if anybody has an information how to get the old data would be perfect, but I am not very optimistic here...
