I tried switching the order of the drives, but this did not help. So then I replaced them in the LaCie enclosure, but they just showed up as 2 different drives which the Mac Mini would not mount. Then I took the pair of 4tb drives from the LaCie and put them in the USB enclosure and switched it to RAID 0 mode, but the Mac Mini did not recognise them. This was set up as a RAID 1 array with 2 2tb drives and I cloned the LaCie contents onto it as a backup. It was originally a RAID 0 array in a LaCie Thunderbolt drive, but this kept randomly dropping out so I decided to move the drives into a COTS USB 3 enclosure instead. This is all on a Mac Mini running High Sierra.
The backups take a long, long time to restore so I'm hoping to be able to rebuild the RAID 0 array instead.
In the process of upgrading a 2 4tb disk RAID 0 array from an iffy LaCie drive to a faster/more reliable USB enclosure I have lost data.
