Hello, I am also quite new to OMV and been struggling with a similar problem. I have 2 disks with 4TB capacity which I want to mount in Raid mirror in OMV. I wiped both disks using using wipefs (because through OMV it would have taken ages) but the disks do not show under the "Create RAID device" option. Both disks are visible under "Disks" tab.
Could anyone give me some advice? I would appreciate it.