[CentOS] samsung sata disk pb

Hi there,

I'm running a centos 5.2 (with a centos 5.3 kernel) on a box with a
samsung 1To green edition, and this disk looks a bit slow to me and it's
not recognized by hdparm :
# hdparm -iI /dev/sda
/dev/sda:
 HDIO_GET_IDENTITY failed: Invalid argument
 HDIO_DRIVE_CMD(identify) failed: Invalid argument

# hdparm -tT /dev/sda
/dev/sda:
 Timing cached reads:   2252 MB in  2.00 seconds = 1125.57 MB/sec
 Timing buffered disk reads:   94 MB in  3.05 seconds =  30.81 MB/sec

I've got a samsung 640go on my desktop running ubuntu (kernel 2.6.27-11),
hdparm -iI is working and benchmark is a lot better :
$ sudo  hdparm -tT /dev/sda
/dev/sda:
 Timing cached reads:   2392 MB in  2.00 seconds = 1196.00 MB/sec
 Timing buffered disk reads:  226 MB in  3.02 seconds =  74.81 MB/sec


the green HD is a 5400rpm, though the other one is 7400rpm, but a factor 2
in performance between them looks very strange to me.
As the green 1 To disk is not identified by hdparm I think it's not
configured properly.

Any hint to make my 1To disk flying like the other one ? :)

cheers,

David