Before thinking of that I would worry about disk13 read errors:
Apr 10 01:12:29 Tower kernel: ata7.00: configured for UDMA/33
Apr 10 01:12:29 Tower kernel: ata7: EH complete
Apr 10 01:12:29 Tower kernel: ata7.00: exception Emask 0x50 SAct 0x8000000 SErr 0x4890800 action 0xe frozen
Apr 10 01:12:29 Tower kernel: ata7.00: irq_stat 0x0c400040, interface fatal error, connection status changed
Apr 10 01:12:29 Tower kernel: ata7: SError: { HostInt PHYRdyChg 10B8B LinkSeq DevExch }
Apr 10 01:12:29 Tower kernel: ata7.00: failed command: READ FPDMA QUEUED
Apr 10 01:12:29 Tower kernel: ata7.00: cmd 60/00:d8:90:37:3a/01:00:00:00:00/40 tag 27 ncq dma 131072 in
Apr 10 01:12:29 Tower kernel: res 40/00:00:90:37:3a/00:00:00:00:00/40 Emask 0x50 (ATA bus error)
Apr 10 01:12:29 Tower kernel: ata7.00: status: { DRDY }
Apr 10 01:12:29 Tower kernel: ata7: hard resetting link
Apr 10 01:12:34 Tower kernel: ata7: link is slow to respond, please be patient (ready=0)
Apr 10 01:12:39 Tower kernel: ata7: COMRESET failed (errno=-16)
Apr 10 01:12:39 Tower kernel: ata7: hard resetting link
Apr 10 01:12:40 Tower kernel: ata7: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
Apr 10 01:12:42 Tower kernel: ata7.00: configured for UDMA/33
Apr 10 01:12:42 Tower kernel: sd 7:0:0:0: [sdo] tag#27 UNKNOWN(0x2003) Result: hostbyte=0x00 driverbyte=0x08
Apr 10 01:12:42 Tower kernel: sd 7:0:0:0: [sdo] tag#27 Sense Key : 0x5 [current]
Apr 10 01:12:42 Tower kernel: sd 7:0:0:0: [sdo] tag#27 ASC=0x21 ASCQ=0x4
Apr 10 01:12:42 Tower kernel: sd 7:0:0:0: [sdo] tag#27 CDB: opcode=0x88 88 00 00 00 00 00 00 3a 37 90 00 00 01 00 00 00
Apr 10 01:12:42 Tower kernel: print_req_error: I/O error, dev sdo, sector 3815312
Apr 10 01:12:42 Tower kernel: md: disk13 read error, sector=3815248
Apr 10 01:12:42 Tower kernel: md: disk13 read error, sector=3815256
Apr 10 01:12:42 Tower kernel: md: disk13 read error, sector=3815264
Apr 10 01:12:42 Tower kernel: md: disk13 read error, sector=3815272
Apr 10 01:12:42 Tower kernel: md: disk13 read error, sector=3815280
Apr 10 01:12:42 Tower kernel: md: disk13 read error, sector=3815288
Apr 10 01:12:42 Tower kernel: md: disk13 read error, sector=3815296
Looks like a connection problem.