smartctl: Raw_Read_Error_Rate very high

[O. Hartmann]

Dear Sirs,

watching from time to time via smartctl my new drives (HITACHI  
HDT722525DLA380 T7K250 250 GB SATA II drives) I found this line on one 
drive (ad4, the 'clean' one is ad4):
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      
UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x000b   100   100   016    Pre-fail  
Always       -       65536


The RAW value of this entry seems to be very high, on the other drives, 
it is zero.

I detected some performance issues within last days, both drives are 
connected as ar0 RAID0 volume to the nForce4 chipset of the ASUS 
A8N32-SLI mainboard.

Any suggestions?

Thanks in advance,

oh