Recently, one of my LaCie rugged drives was acting up, not mounting. So I went to the LaCie site , now owned by Seagate, and downloaded their “toolkit” app. It turned out to be my main drive, also a LaCie “Big” drive, which needed a firmware upgrade. Apparently it was not allowing any other LaCie branded drives to mount regularly. The Toolkit app knew which one needed the firmware upgrade, and it only took a few minutes to do. Now everything is working as expected.
Just a friendly tip for whomever uses LaCie / Seagate external drives.