This bug is related to Bug 462425. I'm openning a new bug by suggestion made there (see comment 462425#85).

The problem is probably a bug in the ata controller driver for some controller chips. My system has:

- Card:   Conceptronic Serial ATA & IDE Combo Card.  (pci card)
- Chip:   VIA Technologies, Inc. VT6421 IDE RAID Controller (rev 50).
- O.S.:   Fedora release 15 (Lovelock).  (32 bits)
- Kernel: 2.6.38.8-32.fc15.i686

Specifically, the problem consists of the communication with the disk being stopped completely, so the sata link has to be reset to begin communication again. In the meantime (since the communication is stopped until the link is reset) (~1 minute), the harddisk is unavailable, so the computer can't read from or write to it. 

The frequency of this problem seems to depend of the disk workload. The more the disk is used, the more the problem appears. As an example, I've forced a high workload by running "cp -va /usr /usr_bk" command, and the result is the problem appearing very frecuently, as you can see in the following syslog (obtained with "dmesg -r"):

---------------
<3>[  381.024060] ata5.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
<3>[  381.024072] ata5.00: failed command: READ DMA EXT
<3>[  381.024087] ata5.00: cmd 25/00:00:28:22:0d/00:01:11:00:00/e0 tag 0 dma 131072 in
<3>[  381.024091]          res 40/00:00:00:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout)
<3>[  381.024098] ata5.00: status: { DRDY }
<6>[  381.024112] ata5: hard resetting link
<6>[  381.329086] ata5: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
<6>[  381.462557] ata5.00: configured for UDMA/133
<4>[  381.462569] ata5.00: device reported invalid CHS sector 0
<6>[  381.462586] ata5: EH complete
<3>[  415.008054] ata5.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
<3>[  415.008066] ata5.00: failed command: READ DMA EXT
<3>[  415.008081] ata5.00: cmd 25/00:00:80:d0:06/00:01:11:00:00/e0 tag 0 dma 131072 in
<3>[  415.008084]          res 40/00:00:00:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout)
<3>[  415.008091] ata5.00: status: { DRDY }
<6>[  415.008105] ata5: hard resetting link
<6>[  415.313091] ata5: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
<6>[  415.425245] ata5.00: configured for UDMA/133
<4>[  415.425257] ata5.00: device reported invalid CHS sector 0
<6>[  415.425273] ata5: EH complete
<3>[  451.008070] ata5.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
<3>[  451.008081] ata5.00: failed command: READ DMA EXT
<3>[  451.008096] ata5.00: cmd 25/00:60:c0:14:0b/00:00:11:00:00/e0 tag 0 dma 49152 in
<3>[  451.008100]          res 40/00:00:00:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout)
<3>[  451.008107] ata5.00: status: { DRDY }
<6>[  451.008121] ata5: hard resetting link
<6>[  451.313104] ata5: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
<6>[  451.420531] ata5.00: configured for UDMA/133
<4>[  451.420542] ata5.00: device reported invalid CHS sector 0
<6>[  451.420558] ata5: EH complete
<4>[  483.002227] ata5.00: limiting speed to UDMA/100:PIO4
<3>[  483.002237] ata5.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
<3>[  483.002247] ata5.00: failed command: READ DMA EXT
<3>[  483.002261] ata5.00: cmd 25/00:e0:40:d2:d4/00:00:10:00:00/e0 tag 0 dma 114688 in
<3>[  483.002264]          res 40/00:00:00:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout)
<3>[  483.002271] ata5.00: status: { DRDY }
<6>[  483.002285] ata5: hard resetting link
<6>[  483.307092] ata5: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
<6>[  483.417269] ata5.00: configured for UDMA/100
<4>[  483.417280] ata5.00: device reported invalid CHS sector 0
<6>[  483.417296] ata5: EH complete
<3>[  517.008060] ata5.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
<3>[  517.008071] ata5.00: failed command: READ DMA EXT
<3>[  517.008086] ata5.00: cmd 25/00:00:40:4a:c8/00:01:10:00:00/e0 tag 0 dma 131072 in
<3>[  517.008089]          res 40/00:00:00:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout)
<3>[  517.008096] ata5.00: status: { DRDY }
<6>[  517.008110] ata5: hard resetting link
<6>[  517.313082] ata5: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
<6>[  517.429945] ata5.00: configured for UDMA/100
<4>[  517.429956] ata5.00: device reported invalid CHS sector 0
<6>[  517.429973] ata5: EH complete
<3>[  563.040060] ata5.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
<3>[  563.040071] ata5.00: failed command: READ DMA EXT
<3>[  563.040086] ata5.00: cmd 25/00:30:b8:32:04/00:00:11:00:00/e0 tag 0 dma 24576 in
<3>[  563.040090]          res 40/00:00:00:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout)
<3>[  563.040097] ata5.00: status: { DRDY }
<6>[  563.040111] ata5: hard resetting link
<6>[  563.345080] ata5: SATA link up 1.5 Gbps (SStatus 113 SControl 310)
<6>[  563.513241] ata5.00: configured for UDMA/100
<4>[  563.513251] ata5.00: device reported invalid CHS sector 0
<6>[  563.513266] ata5: EH complete
---------------

I'm sure my sata disk drive is ok (I've tested it with other controller and no
errors appear). So the problem is at the controller hardware, or at the
controller driver. I bet it's at the controller driver.

Thanks