fsck unable to read disk sectors

hi there,

when doing fsck on my / fs i get this error:

"Cannot Read BLK. 471617640" and "The Following Disk Sectors could not be
read: 471617643". after this message the partition gets marked dirty.

i performed the following steps to verify the problem:

1) dd if=/dev/ada0 of=/dev/null bs=1m
2) fsck / under freebsd 7
3) mount -u -o snapshot /.snap/snapshot1 / && fsck_ffs /.snap/snapshot1

all three steps showed no problem with that harddrive whatsoever. also smartd
doesn't complain about anything.

i'm running HEAD (r205860) on amd64.

this is the output of `dmesg -a|grep ada0`:

ada0 at ahcich2 bus 0 scbus3 target 0 lun 0
ada0: <SAMSUNG SP2504C VT100-50> ATA-7 SATA 2.x device
ada0: 300.000MB/s transfers (SATA 2.x, UDMA6, PIO 8192bytes)
ada0: Command Queueing enabled
ada0: 238474MB (488395055 512 byte sectors: 16H 63S/T 16383C)

-- 
Alexander Best