I got a WD4000KD belived to be faulty. SMART data reveals it has 16 reallocated sectors (not a big problem since power-on hours is about 20.000), and it had about 25 offline scan uncorrectable sectors. WD Data Lifeguard of course considered the drive as failed as well, since the smart self test failed with a read error.
I made a 3-pass zerofill and the drive seems to work perfectly, no bad sectors or anything, however, offline scan uncorrectable count is 2, according to SMART. Here comes the interesting part. SMART Self Test Log:
Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error
# 1 Short offline Completed: read failure 20% 22134 781420654
You can see that the sector still problemous is 781.420.654. If I open the drive in disc editor, the last sector I can access 781.419.680. More interesting: looking at Everest, it stated that the HDD has a total sectors of 781.420.655. This would mean that the last two sector of the HDD is unreadable, but I cannot access them. To make it even more complicated, WD's data sheet of the drive states 781.422.768.
Other uncorrectable sectors were repaired by overwrite, so I could have a perfect drive if I would be able to overwrite the sector(s) in question, but seems like they are not accessible by the user, that's why chkdsk and any other surface test does not reveal any errors.
What do you think?