Write-cache problems

For anyone interested, here is my syslog data after the UPS kicked in on a power fail:

Jan 19 15:20:46 MainStore RAIDiator: UPS has been disconnected.
Jan 19 15:20:46 MainStore RAIDiator: UPS has been disconnected.\n[Thu Jan 19 15:20:46 WET 2012]
Jan 19 15:20:53 MainStore hidups[11836]: Startup successful
Jan 19 15:20:55 MainStore upsd[11843]: Connected to UPS [UPS]: hidups-hiddev0
Jan 19 15:20:55 MainStore upsd[11844]: Startup successful
Jan 19 15:20:56 MainStore upsmon[11857]: Startup successful
Jan 19 15:20:56 MainStore upsmon[11857]: Warning: running as one big root process by request (upsmon -p)
Jan 19 15:20:56 MainStore upsd[11844]: Client monuser@127.0.0.1 logged into UPS [UPS]
Jan 19 15:20:56 MainStore kernel: ata1.00: configured for UDMA/133
Jan 19 15:20:56 MainStore kernel: ata1: EH complete
Jan 19 15:20:56 MainStore kernel: sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
Jan 19 15:20:56 MainStore kernel: ata2.00: configured for UDMA/133
Jan 19 15:20:56 MainStore kernel: ata2: EH complete
Jan 19 15:20:56 MainStore kernel: sd 1:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
Jan 19 15:20:56 MainStore kernel: ata3.00: configured for UDMA/133
Jan 19 15:20:56 MainStore kernel: ata3: EH complete
Jan 19 15:20:56 MainStore kernel: sd 2:0:0:0: [sdc] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
Jan 19 15:20:56 MainStore kernel: ata4.00: configured for UDMA/133
Jan 19 15:20:56 MainStore kernel: ata4: EH complete
Jan 19 15:20:56 MainStore kernel: sd 3:0:0:0: [sdd] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
Jan 19 15:20:56 MainStore kernel: ata5.00: configured for UDMA/133
Jan 19 15:20:56 MainStore kernel: ata5: EH complete
Jan 19 15:20:56 MainStore kernel: sd 4:0:0:0: [sdd] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
Jan 19 21:20:21 MainStore kernel: ata4.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
Jan 19 21:20:21 MainStore kernel: ata4.00: failed command: FLUSH CACHE EXT
Jan 19 21:20:21 MainStore kernel: ata4.00: cmd ea/00:00:00:00:00/00:00:00:00:00/a0 tag 0
Jan 19 21:20:21 MainStore kernel: res 40/00:01:00:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout)
Jan 19 21:20:21 MainStore kernel: ata4.00: status: { DRDY }
Jan 19 21:20:21 MainStore kernel: ata4: hard resetting link
Jan 19 21:20:22 MainStore kernel: ata4: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
Jan 19 21:20:22 MainStore kernel: ata4.00: configured for UDMA/133
Jan 19 21:20:22 MainStore kernel: ata4.00: retrying FLUSH 0xea Emask 0x4
Jan 19 21:20:22 MainStore kernel: ata4.00: device reported invalid CHS sector 0
Jan 19 21:20:22 MainStore kernel: ata4: EH complete
Jan 19 21:32:24 MainStore kernel: ata4.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6 frozen
Jan 19 21:32:24 MainStore kernel: ata4.00: failed command: FLUSH CACHE EXT
Jan 19 21:32:24 MainStore kernel: ata4.00: cmd ea/00:00:00:00:00/00:00:00:00:00/a0 tag 0
Jan 19 21:32:24 MainStore kernel: res 40/00:01:00:4f:c2/00:00:00:00:00/00 Emask 0x4 (timeout)
Jan 19 21:32:24 MainStore kernel: ata4.00: status: { DRDY }

Note that one of my Seagate disks (ata4/sd3) froze at 21:20. This would not of occured had disk-write cache not been magically turned back on.