by hdsentinel » 2020.12.15. 15:50
Yes, as you wrote: when the hard disk finds a problematic sector, it may try the re-allocation procedure: during that, the hard disk attempts to recover the data and copy to a spare sector. Then all further reads/writes are redirected to this spare area, the original bad sector is no longer accessible. Ideally the drive then work like "perfect".
This is described at:
https://www.hdsentinel.com/faq.php#health
But this may not happen automatically, the sector can damage when it contains your data. Then the sector will be unreadable and the hard disk usually does not perform automatic reallocation at this point: the sector become damaged (weak / pending) and we'd need to "help" the hard disk to restore the status to normal - or to perform the reallocation.
These sectors usually (incorrectly) identified as "bad sectors" by chkdsk which does not perform real fix.
This is described at:
https://www.hdsentinel.com/hard_disk_case_weak_sectors.php
The problem is that the reallocation is not always possible: in many cases, the contents of the affected sector is lost and even in the best outcome, you may expect a not stable operation and lower performance as the drive may "stuck" for longer time during reallocation (especially if there are multiple sectors affected).
Also when your hard disk has 100's (or even more) bad sectors already reallocated, then the chances of possible further problems (data corruption, data loss or even failure) higher. This is why we can accept some bad sectors - but not too many.
And in case of any degradation (one or more new bad sector detected) the best is to perform intensive testing to reveal possible further - and stabilize them, as described at
https://www.hdsentinel.com/faq.php#tests
and
https://www.hdsentinel.com/faq_repair_hard_disk_drive.php
