On 11/3/2010 8:32 AM, Keith Roberts wrote: > > So to prepare the disk for returning under warranty, I used > another HDD utility to clean the disk again ... > So I ran an Advanced r/w scan again with Hitachi DFT, and > the result was OK. A complete disk wipe brings bad sectors to the drive's attention, forcing it to remap them using spare sectors set aside for the purpose. All drives can do this, and they do it without logging the change. You can't tell, from the outside, when or whether the drive has done this. All you can do is infer it, because a sector that once tested bad now tests good. As to why this happened only during a format, not during the previous disk test, it's probably because the format zeroed the disk. That particular drive may have a policy to only remap sectors on write, so as to preserve the sector contents for potential recovery later. (See below for one way this can be done.) It may be that your drive is now fine. If you put it back into service, at minimum I would set up smartd, from the smartmontools package. Maybe run smartctl on it by hand daily or weekly, too. If you find that errors start happening again, there is something continually degrading the drive's integrity, so the automatic sector remapping will eventually run the drive out of spare sectors. SpinRite (http://spinrite.com/) does nondestructive sector remapping. At level 4 and above, it reads each sector in and then writes it back out to the drive. Because remapping is silent, it's possible for it to appear to do nothing, yet improve data integrity by bringing dodgy sectors to the drive's attention. If a sector can't be read without error, SpinRite forces the drive to ignore the CRC and return the data anyway, retrying many times, then making a statistical guess about the most likely contents of the sector. (Reading a bad sector won't necessarily give the same value each try.) Then on writing the reconstructed data back out, the drive automatically remaps the sector, repairing it. You might want to combine the SMART monitoring with periodic SpinRite runs on the drive until you regain confidence in it.