So, to End that all:
I had some Problems because my Trial was Expired so i tried to get these 14 Days Extension, but there was some Server Error, so i Bought an Licence-Key for the OS.
I followed your Instructions @jonp and moved many Files from here to there .I was migrating two Running 8tb Raid 1 OMV Drives into this System. (Basically i installed one as Drive in the Array and Copied the Files via Windows SMB Drag and Drop [Raspberry PI -> Windows -> "Chantal"] ).
Then i copied my Old disk 1 on an other, same sized btrfs Drive in an Cache pool, formated the old cache drive and added it to the pool. Now i have an great redundancy for my Cache and my Normal 2 Drives
Scr of Current Setup :
Thx for all the Help, and have a nice Day