[CentOS] Disk error

For some time I have been seeing disk errors in the syslog every seven days.  Until today it always happens Sunday morning at 8:13 AM, plus or minus a minute or two.  Yesterday it happened at 1:13 AM.  Here are the pertinent log entries for the latest occurrence:

Jan  6 01:12:29 g2 kernel: ata9.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jan  6 01:12:29 g2 kernel: ata9.00: BMDMA stat 0x64
Jan  6 01:12:29 g2 kernel: ata9.00: failed command: READ DMA EXT
Jan  6 01:12:29 g2 kernel: ata9.00: cmd 25/00:00:00:fe:d5/00:02:04:00:00/e0 tag 0 dma 262144 in
Jan  6 01:12:29 g2 kernel:         res 51/40:00:19:ff:d5/40:00:04:00:00/00 Emask 0x9 (media error)
Jan  6 01:12:29 g2 kernel: ata9.00: status: { DRDY ERR }
Jan  6 01:12:29 g2 kernel: ata9.00: error: { UNC }
Jan  6 01:12:29 g2 kernel: ata9.00: configured for UDMA/33
Jan  6 01:12:29 g2 kernel: ata9.01: configured for UDMA/33
Jan  6 01:12:29 g2 kernel: ata9: EH complete
Jan  6 01:12:33 g2 kernel: ata9.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jan  6 01:12:33 g2 kernel: ata9.00: BMDMA stat 0x64
Jan  6 01:12:33 g2 kernel: ata9.00: failed command: READ DMA EXT
Jan  6 01:12:33 g2 kernel: ata9.00: cmd 25/00:00:00:fe:d5/00:02:04:00:00/e0 tag 0 dma 262144 in
Jan  6 01:12:33 g2 kernel:         res 51/40:00:7c:ff:d5/40:00:04:00:00/00 Emask 0x9 (media error)
Jan  6 01:12:33 g2 kernel: ata9.00: status: { DRDY ERR }
Jan  6 01:12:33 g2 kernel: ata9.00: error: { UNC }
Jan  6 01:12:33 g2 kernel: ata9.00: configured for UDMA/33
Jan  6 01:12:33 g2 kernel: ata9.01: configured for UDMA/33
Jan  6 01:12:33 g2 kernel: ata9: EH complete
Jan  6 01:13:06 g2 kernel: ata9.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jan  6 01:13:06 g2 kernel: ata9.00: BMDMA stat 0x64
Jan  6 01:13:06 g2 kernel: ata9.00: failed command: READ DMA EXT
Jan  6 01:13:06 g2 kernel: ata9.00: cmd 25/00:00:00:bf:d6/00:02:04:00:00/e0 tag 0 dma 262144 in
Jan  6 01:13:06 g2 kernel:         res 51/40:00:db:bf:d6/40:00:04:00:00/00 Emask 0x9 (media error)
Jan  6 01:13:06 g2 kernel: ata9.00: status: { DRDY ERR }
Jan  6 01:13:06 g2 kernel: ata9.00: error: { UNC }
Jan  6 01:13:07 g2 kernel: ata9.00: configured for UDMA/33
Jan  6 01:13:07 g2 kernel: ata9.01: configured for UDMA/33
Jan  6 01:13:07 g2 kernel: ata9: EH complete
Jan  6 01:13:10 g2 kernel: ata9.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jan  6 01:13:10 g2 kernel: ata9.00: BMDMA stat 0x64
Jan  6 01:13:10 g2 kernel: ata9.00: failed command: READ DMA EXT
Jan  6 01:13:10 g2 kernel: ata9.00: cmd 25/00:00:00:bf:d6/00:02:04:00:00/e0 tag 0 dma 262144 in
Jan  6 01:13:10 g2 kernel:         res 51/40:00:db:bf:d6/40:00:04:00:00/00 Emask 0x9 (media error)
Jan  6 01:13:10 g2 kernel: ata9.00: status: { DRDY ERR }
Jan  6 01:13:10 g2 kernel: ata9.00: error: { UNC }
Jan  6 01:13:10 g2 kernel: ata9.00: configured for UDMA/33
Jan  6 01:13:10 g2 kernel: ata9.01: configured for UDMA/33
Jan  6 01:13:10 g2 kernel: ata9: EH complete
Jan  6 01:13:14 g2 kernel: ata9.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jan  6 01:13:14 g2 kernel: ata9.00: BMDMA stat 0x64
Jan  6 01:13:14 g2 kernel: ata9.00: failed command: READ DMA EXT
Jan  6 01:13:14 g2 kernel: ata9.00: cmd 25/00:00:00:bf:d6/00:02:04:00:00/e0 tag 0 dma 262144 in
Jan  6 01:13:14 g2 kernel:         res 51/40:00:db:bf:d6/40:00:04:00:00/00 Emask 0x9 (media error)
Jan  6 01:13:14 g2 kernel: ata9.00: status: { DRDY ERR }
Jan  6 01:13:14 g2 kernel: ata9.00: error: { UNC }
Jan  6 01:13:14 g2 kernel: ata9.00: configured for UDMA/33
Jan  6 01:13:14 g2 kernel: ata9.01: configured for UDMA/33
Jan  6 01:13:14 g2 kernel: ata9: EH complete
Jan  6 01:13:17 g2 kernel: ata9.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jan  6 01:13:17 g2 kernel: ata9.00: BMDMA stat 0x64
Jan  6 01:13:17 g2 kernel: ata9.00: failed command: READ DMA EXT
Jan  6 01:13:17 g2 kernel: ata9.00: cmd 25/00:00:00:bf:d6/00:02:04:00:00/e0 tag 0 dma 262144 in
Jan  6 01:13:17 g2 kernel:         res 51/40:00:db:bf:d6/40:00:04:00:00/00 Emask 0x9 (media error)
Jan  6 01:13:17 g2 kernel: ata9.00: status: { DRDY ERR }
Jan  6 01:13:17 g2 kernel: ata9.00: error: { UNC }
Jan  6 01:13:18 g2 kernel: ata9.00: configured for UDMA/33
Jan  6 01:13:18 g2 kernel: ata9.01: configured for UDMA/33
Jan  6 01:13:18 g2 kernel: ata9: EH complete
Jan  6 01:13:21 g2 kernel: ata9.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jan  6 01:13:21 g2 kernel: ata9.00: BMDMA stat 0x64
Jan  6 01:13:21 g2 kernel: ata9.00: failed command: READ DMA EXT
Jan  6 01:13:21 g2 kernel: ata9.00: cmd 25/00:00:00:bf:d6/00:02:04:00:00/e0 tag 0 dma 262144 in
Jan  6 01:13:21 g2 kernel:         res 51/40:00:db:bf:d6/40:00:04:00:00/00 Emask 0x9 (media error)
Jan  6 01:13:21 g2 kernel: ata9.00: status: { DRDY ERR }
Jan  6 01:13:21 g2 kernel: ata9.00: error: { UNC }
Jan  6 01:13:21 g2 kernel: ata9.00: configured for UDMA/33
Jan  6 01:13:21 g2 kernel: ata9.01: configured for UDMA/33
Jan  6 01:13:21 g2 kernel: ata9: EH complete
Jan  6 01:13:25 g2 kernel: ata9.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
Jan  6 01:13:25 g2 kernel: ata9.00: BMDMA stat 0x64
Jan  6 01:13:25 g2 kernel: ata9.00: failed command: READ DMA EXT
Jan  6 01:13:25 g2 kernel: ata9.00: cmd 25/00:00:00:bf:d6/00:02:04:00:00/e0 tag 0 dma 262144 in
Jan  6 01:13:25 g2 kernel:         res 51/40:00:db:bf:d6/40:00:04:00:00/00 Emask 0x9 (media error)
Jan  6 01:13:25 g2 kernel: ata9.00: status: { DRDY ERR }
Jan  6 01:13:25 g2 kernel: ata9.00: error: { UNC }
Jan  6 01:13:25 g2 kernel: ata9.00: configured for UDMA/33
Jan  6 01:13:25 g2 kernel: ata9.01: configured for UDMA/33
Jan  6 01:13:25 g2 kernel: sd 8:0:0:0: [sdg] Unhandled sense code
Jan  6 01:13:25 g2 kernel: sd 8:0:0:0: [sdg] Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE
Jan  6 01:13:25 g2 kernel: sd 8:0:0:0: [sdg] Sense Key : Medium Error [current] [descriptor]
Jan  6 01:13:25 g2 kernel: Descriptor sense data with sense descriptors (in hex):
Jan  6 01:13:25 g2 kernel:        72 03 11 04 00 00 00 0c 00 0a 80 00 00 00 00 00
Jan  6 01:13:25 g2 kernel:        04 d6 bf db
Jan  6 01:13:25 g2 kernel: sd 8:0:0:0: [sdg] Add. Sense: Unrecovered read error - auto reallocate failed
Jan  6 01:13:25 g2 kernel: sd 8:0:0:0: [sdg] CDB: Read(10): 28 00 04 d6 bf 00 00 02 00 00
Jan  6 01:13:25 g2 kernel: ata9: EH complete

There is nothing in /etc/cron.weekly, nor are there any root crontab entries.  Any suggestions for investigating this issue would be much appreciated.

Emmett