In fact, both disks passed the 'smartctl -a' test
That's not a test, that's querying the disk's status. Run smartctl -s on -o on -S on once per disk. This enables smart and the disk's offline selftests. Any bad sectors found here show up as offline_uncorrectable. There was an excellent discusion on this on the smartmontool-users list over the last days. Run the short and long tests, -t short and -t long, waiting for each to finish. Then run smartctl -a and check for errors.
/dev/hde, SMART Prefailure Attribute: 8 Seek_Time_Performance changed from 249 to 250
In the sum, these attributes are a measure for the disk's health. Each by themselves is meaningless unless it's right at the diabolical end. You'll probably find this one cycles between 249 and 250. smartd just logs each change. Bruce Allen is always looking for people to program more intelligence into smartd ;) Volker -- Volker Kuhlmann is possibly list0570 with the domain in header http://volker.dnsalias.net/ Please do not CC list postings to me.