New question but related to this topic: I used xfs_repair on one of the 2 drives that were failing/failed. The other drive died completely and wasn't seen by any OS or even at the BIOS level.   I made an image of the 4TB XFS partition using ddrescue before attempting use of xfs_repair.  As reported here, that image isn't mountable. While the xfs_repair run did appear to recover the data from the drive into the 'lost+found' folder, there are still a number of files/folders that are miss