Ubuntu 12.04 (but the same was on 11.10 before upgrading)

WD MyBook, 2TB, no RAID (or RAID0, not completely sure, anyway no mirroring, both 1TB disks are in use, mounted as a single device). Formatted to XFS, normally used for big movie files. Connected to Firewire 800.

At some point the LED started going up and down as when constantly reading/writing. The device gives access error.

When unplugged (cable, then holding the power button for a while, then unplugging the power) and re-connected becomes available. xfs_check with no results. xfs_repair did something, but looks like didn't fix any error.

Then after a massive read (checking 1.5GB torrent file for integrity) becomes unavailable again.

Any ideas what's wrong? Drives? Cables? Motherboard? OS?

UPD: not sure how relevant this is, but here are dmesg output

[14380.632816] SGI XFS with ACLs, security attributes, realtime, large block/inode numbers, no debug enabled
[14380.633356] SGI XFS Quota Management subsystem
[14421.812220] firewire_core: phy config: card 0, new root=ffc1, gap_count=5
[14441.890596] firewire_core: phy config: card 0, new root=ffc1, gap_count=5
[14441.896858] firewire_core: phy config: card 0, new root=ffc1, gap_count=5
[14453.895347] firewire_core: created device fw1: GUID 0090a99500a35518, S400, 9 config ROM retries
[14453.904818] scsi6 : SBP-2 IEEE-1394
[14453.905014] scsi7 : SBP-2 IEEE-1394
[14454.139993] firewire_sbp2: fw1.0: logged in to LUN 0000 (0 retries)
[14454.158769] scsi 6:0:0:0: Direct-Access     WD       My Book          1015 PQ: 0 ANSI: 4
[14454.159251] sd 6:0:0:0: Attached scsi generic sg3 type 0
[14454.162391] firewire_sbp2: fw1.1: logged in to LUN 0001 (0 retries)
[14454.167453] sd 6:0:0:0: [sdc] 3907017568 512-byte logical blocks: (2.00 TB/1.81 TiB)
[14454.178822] sd 6:0:0:0: [sdc] Write Protect is off
[14454.178826] sd 6:0:0:0: [sdc] Mode Sense: 10 00 00 00
[14454.186830] scsi 7:0:0:1: Enclosure         WD       My Book Device   1015 PQ: 0 ANSI: 4
[14454.186995] scsi 7:0:0:1: Attached scsi generic sg4 type 13
[14454.190078] sd 6:0:0:0: [sdc] Cache data unavailable
[14454.190087] sd 6:0:0:0: [sdc] Assuming drive cache: write through
[14454.202176] sd 6:0:0:0: [sdc] Cache data unavailable
[14454.202185] sd 6:0:0:0: [sdc] Assuming drive cache: write through
[14454.239940]  sdc: [mac] sdc1 sdc2 sdc3 sdc4
[14454.271262] sd 6:0:0:0: [sdc] Cache data unavailable
[14454.271270] sd 6:0:0:0: [sdc] Assuming drive cache: write through
[14454.271354] sd 6:0:0:0: [sdc] Attached SCSI disk
[14454.272149] ses 7:0:0:1: Attached Enclosure device
[14606.090024] XFS (sdc3): Mounting Filesystem
[14612.048343] XFS (sdc3): Starting recovery (logdev: internal)
[14620.697636] XFS (sdc3): Ending recovery (logdev: internal)
[14748.120957] e1000e: eth0 NIC Link is Up 100 Mbps Full Duplex, Flow Control: Rx/Tx
[14748.120963] e1000e 0000:00:19.0: eth0: 10/100 speed: disabling TSO
[14752.568382] uhci_hcd 0000:00:1a.0: PCI INT A disabled
[14752.568579] uhci_hcd 0000:00:1a.1: PCI INT B disabled
[14752.568738] ehci_hcd 0000:00:1a.7: PCI INT C disabled
[14752.568779] ehci_hcd 0000:00:1a.7: PME# enabled
[14752.584526] uhci_hcd 0000:00:1d.1: PCI INT B disabled
[14752.584689] uhci_hcd 0000:00:1d.2: PCI INT C disabled
[14752.680079] ehci_hcd 0000:00:1a.7: BAR 0: set to [mem 0xe4641000-0xe46413ff] (PCI address [0xe4641000-0xe46413ff])
[14752.680104] ehci_hcd 0000:00:1a.7: restoring config space at offset 0xf (was 0x300, writing 0x30b)
[14752.680136] ehci_hcd 0000:00:1a.7: restoring config space at offset 0x1 (was 0x2900000, writing 0x2900002)
[14752.680170] ehci_hcd 0000:00:1a.7: PME# disabled
[14752.680182] ehci_hcd 0000:00:1a.7: PCI INT C -> GSI 18 (level, low) -> IRQ 18
[14752.680190] ehci_hcd 0000:00:1a.7: setting latency timer to 64
[14752.710334] uhci_hcd 0000:00:1a.0: PCI INT A -> GSI 16 (level, low) -> IRQ 16
[14752.710342] uhci_hcd 0000:00:1a.0: setting latency timer to 64
[14752.749186] uhci_hcd 0000:00:1a.1: PCI INT B -> GSI 17 (level, low) -> IRQ 17
[14752.749194] uhci_hcd 0000:00:1a.1: setting latency timer to 64
[14752.790231] uhci_hcd 0000:00:1d.1: PCI INT B -> GSI 22 (level, low) -> IRQ 22
[14752.790239] uhci_hcd 0000:00:1d.1: setting latency timer to 64
[14752.829170] uhci_hcd 0000:00:1d.2: PCI INT C -> GSI 18 (level, low) -> IRQ 18
[14752.829178] uhci_hcd 0000:00:1d.2: setting latency timer to 64