ATA abnormal status

[Francesco Pietra <frapietra@alice.it>]

While computing with mpqc2.3.1 (debian etch amd6a; dual opterons; 8GB ram ECC; 
raid 1; filesystem ext3; grub on its own partition):

Led of HD permanently lighted.

Messages on screen:

ATA: abnormal status 0x58 on port 0x1C5F
ata3: command 0x35 timeout, stat 0x50 host_stat 0x24
ata 4: same as above for ata3

Trying:
$ df -h

sd 3:0:0:0 SCSI error return code 0x8000002
Additional sense : SCSI parity error
end request: I/O error, dev sda, sector 47748992

Later:
raid1 Disk failure on sd6, disabling device
raid1 :sdb3: redirecting another mirror

RAID1 conf printout
--- wd:1 rd:2
disk1, wo:0, o:1, dev: sdb8
_______

I cold only switch power off because it did not respond to down commands.
_______

Rebooting, the $ prompt was obtained without warnings.

Then I looked at
 /etc/fstab

and issued:

#fdisk /dev/sda
# p
#fdisk /dev/sdb
# p
#df -h

there was nothing wrong: both disks identical to before.
______________________________

Similar hanging already occurred on 3 August (it was already ext3 filesystem) 
during similar computation with mpqc. There was nothing wrong after rebooting 
and up to now there was no anomaly. I checked disks and ram.

Before that, when using raiser 3.6 filesystem, I had many problems with debian 
while carrying out mpqc computations . Therefore, I changed to ext3.

Thread computations with mpqc for without interruption many days are big 
stress to the system (mostly for memory because mpqc writes sparingly on HD).
___________--

Any guess at what that means? I naively understand it was failure by the OS, 
not failure of hardware.

Thank you for reading this long report.

Cheers

francesco pietra