This is very strange, clearly there's a xfs filesystem on disk2:
ep 29 20:00:48 FILE-SERVER kernel: XFS (md2): Mounting V5 Filesystem
Sep 29 20:00:48 FILE-SERVER root: mount: /mnt/disk2: mount(2) system call failed: Structure needs cleaning.
Sep 29 20:00:48 FILE-SERVER root: dmesg(1) may have more information after failed mount system call.
Sep 29 20:00:48 FILE-SERVER kernel: XFS (md2): Log inconsistent (didn't find previous header)
Sep 29 20:00:48 FILE-SERVER kernel: XFS (md2): failed to find log head
Sep 29 20:00:48 FILE-SERVER kernel: XFS (md2): log mount/recovery failed: error -117
Sep 29 20:00:48 FILE-SERVER kernel: XFS (md2): log mount failed
But xfs_repair doesn't find main or a backup superblock, something weird is happening there, just one last shot in the dark, and to rule out any md driver issue, with the array stopped type in the console:
xfs_repair -v /dev/sdc1