Xen users - Apr 2008 - disk i/o errors on Dom0 "kills" all DomU''s

I''m trying to do ''naughty'' things with a DVD on my
Centos 5.1 Dom0,
and my punishment is non-responsive DomU''s.

I am running DVD:RIP as a normal user on the Dom0, with a disc that
has bad sectors or something, so it''s having a hard time reading it.
All the DomU''s instantly become very slow to completely non
responsive.  Running the same app on a dvd that''s not been
purposefully corrupted, all is well.

It doesn''t seem to matter if the DomU is PVM or FVM(hvm?),
they''re
both degraded.  The DomU OS doesn''t seem to matter either, I have
several centos domu''s and a few windows xp / server 2003
domu''s.

As far as I can tell, the server is not struggling, the cpu shows
barely above 5% utilization, the memory usage is very slow and iostat
-x doesn''t show any wait times for any of the disks.

So why do the DomU''s slip into comas when Dom0 is having a hard time
reading a disc?

My optical drive is a Toshiba 18X dvd-ram, parallel ata connected.  It
is the only pata device on the box, I have ten more hard drives
connected to various SATA2 ports.  The box is powered by a Xeon e5405
with 8g of ram.  The host OS is 64 bit centos 5.1, running the
''stock''
redhat version of xen (3.1 i believe).

Any suggestions?

Gordon

from dmesg:

hda: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hda: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
hda: cdrom_decode_status: status=0x51 { DriveReady SeekComplete Error }
hda: cdrom_decode_status: error=0x40 { LastFailedSense=0x04 }
ide: failed opcode was: unknown
(snip)
hda: ide_intr: huh? expected NULL handler on exit
hda: ATAPI reset complete
end_request: I/O error, dev hda, sector 4145744
Buffer I/O error on device hda, logical block 1036436
Buffer I/O error on device hda, logical block 1036437
Buffer I/O error on device hda, logical block 1036438
Buffer I/O error on device hda, logical block 1036439
Buffer I/O error on device hda, logical block 1036440
(snip)
hda: ATAPI reset complete
end_request: I/O error, dev hda, sector 4146000
printk: 54 messages suppressed.
Buffer I/O error on device hda, logical block 1036500
(snip)
ide: failed opcode was: unknown
ATAPI device hda:
  Error: Medium error -- (Sense key=0x03)
  (reserved error code) -- (asc=0x11, ascq=0x05)
  The failed "Read 10" packet command was:
  "28 00 00 04 0a 78 00 00 40 00 00 00 00 00 00 00 "
end_request: I/O error, dev hda, sector 1059368
cdrom: hda: mrw address space DMA selected
cdrom: hda: mrw address space DMA selected

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