Apologies. I was unable to edit the post here, and in my tiredness got the wrong digit.

They are RAID1 (Mirror) arrays.

I could not re-add the disk, as Open-E labelled it as active as a "S/W RAID Part", but not part of any active array.

I have re-written my flash drive with the latest version of OpenE and still cannot boot with any disks connected except for one.

One booted I can re-add disks, but it is fraught with problems, sometimes it works, sometimes it doesn't.

Currently on bootup with 4 drives connected I get UNKNOWN OPERAND again. On shutdown, sometimes it crashes with a white screen of death.

Commercial deployment at this point looks highly unlikely, which is just my luck.