bad sectors, suspicious behaviour

Hello!

I'm not sure  I chose correct maillist, so point me somewhere in case of 
mistake :)

I'm trying to emulate OS behaviour when something goes wrong with sata 
hard drive, for example, unrecoverable "bad blocks".
By some reason I do not want to use any sw/hw raid.

I took new hard drive, because it should contain (and it contains) 
unreadable (not reallocated yet) sectros, and did


'dd if=/dev/sda of=/dev/null bs=1M'. 

first run dd log (errors1.txt) looks OK, drive recovers, as I suppose, 
approximately at time

cat 
/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:02.0/host4/target4:0:0/4:0:0:0/timeout
30

but when running dd second time, log looks strange (errors2.txt)


running
echo 1 > 
/sys/devices/pci0000:00/0000:00:01.0/0000:01:00.0/0000:02:02.0/host4/target4:0:0/4:0:0:0/delete
echo "scsi add-single-device 4 0 0 0" > /proc/scsi/scsi

and then running dd solve situation until next dd

It is vanilla 2.6.26.2 kernel and sata_mv (MV88SX6081 8-port SATA II PCI-X)