CURRENT: (ada1:ahcich9:0:0:0): READ_FPDMA_QUEUED. ACB: 60 00 54 5e 83 40 4e 00

On a machine running  FreeBSD 10.0-ALPHA4 #0 r256044: Fri Oct  4
11:48:43 CEST 2013 amd64 I get the follwoing message very frequently
when a small tool is extracting data stored on a ZFS JBOD comprised of
two disks:

errors: No known data errors

  pool: POOL00
 state: ONLINE
status: One or more devices has experienced an error resulting in data
        corruption.  Applications may be affected.
action: Restore the file in question if possible.  Otherwise restore the
        entire pool from backup.
   see: http://illumos.org/msg/ZFS-8000-8A
  scan: scrub repaired 0 in 12h8m with 1 errors on Tue Sep 24 10:34:26
  2013
config:

        NAME        STATE     READ WRITE CKSUM
        POOL00      ONLINE       0     0     5
          ada1p1    ONLINE       0     0    10  block size: 512B
        configured, 4096B native
          ada2p1    ONLINE       0     0    10  block size: 512B
        configured, 4096B native

errors: 2 data errors, use '-v' for a list

The dmesg on the eroror is:

(ada1:ahcich9:0:0:0): READ_FPDMA_QUEUED. ACB: 60 00 54 5e 83 40 4e 00
00 01 00 00 (ada1:ahcich9:0:0:0): CAM status: ATA Status Error
(ada1:ahcich9:0:0:0): ATA status: 41 (DRDY ERR), error: 40 (UNC )
(ada1:ahcich9:0:0:0): RES: 41 40 f8 5e 83 40 4e 00 00 00 00
(ada1:ahcich9:0:0:0): Retrying command


The error in the POOL00 (ZFS) seems to be sticky, since I tried to
delete the files reported corrupted, but this problem of damaged data
isn't serious and it has been for a while. What really confuses is the
new CAM related message and I'd like to ask whether this could be the
preludium of a serious hardware failure.

Thanks in advance,

Oliver