Looking at this from the HexOS side - I have a 2-disk mirror where one of the drives has failed and the other is warning (let this be a lesson that similar drives brought into service at the same time have a tendency to die around the same time...assuming they survive infant death periods).
When I click "Replace", I get this nice popup that says to "Select a replacement from one of your currently matching unused drives below...". Only I don't have any unused drives and none that match the failed one in the system, used or otherwise. I have a perfect replacement sitting here on my desk. What do?