I have an external storage with 2 x 2TB ( Stardom 2Bay, JBOD mode ) that was working nicely with my Macmini . Somehow since last week the disk is not readable anymore. I got the message that " The disk you inserted was not readable by this computer " and it asked to "Initialize", "Ignore" or "" Eject". OS is the newest El Cpatian (10.11.5) and I've tried other enclosure and docking station and all saw the same message. I also tried multiple computers (MBAs, MB, PC Win 7) and the same issue. I then started trying to repair it on Terminal: "diskutil list" showed me the disk is now disk3 without partition. So I did this first: sudo diskutil verifyVolume /dev/disk3 and I got the error message: " Error starting file system verification for disk3: Unrecognized file system (-69846)" . Then I used "sudo fsck_exfat -d /dev/disk3". Now I got the message: "Opening /dev/rdisk3 ** Checking volume. ** Checking main boot region. fsck_exfat: Invalid jump or signature Main boot region is invalid. Trying alternate boot region. ** Checking alternate boot region. fsck_exfat: Invalid jump or signature Alternate boot region is invalid. ** The volume could not be verified completely." So now how am I supposed to fix this? Thanks for your suggestions.