Disks are not mounting because of read errors:
Mar 27 15:05:58 Media kernel: md: disk13 read error, sector=8590653888
Mar 27 15:05:58 Media kernel: md: disk13 read error, sector=8590653896
Mar 27 15:05:58 Media kernel: md: disk13 read error, sector=8590653904
...
Mar 27 15:05:58 Media kernel: md: disk14 read error, sector=8590548952
Mar 27 15:05:58 Media kernel: md: disk14 read error, sector=8590548960
Mar 27 15:05:58 Media kernel: md: disk14 read error, sector=8590548968
..
Mar 27 15:05:59 Media kernel: md: disk16 read error, sector=8592953024
Mar 27 15:05:59 Media kernel: md: disk16 read error, sector=8592953032
Mar 27 15:05:59 Media kernel: md: disk16 read error, sector=8592953040
etc, check what they have in common, controller, expander, etc, there's likely a problem with one of those.