In case the verification fails or the sector is deemed unreliable by the firmware, the firmware can immediately replace the sector so no user data is lost(at least not lost at the moment it is written to disk surface). When HDD writes a sector, it does read verification immediately(verify CRC checksum and employ ECC to recover the soft error bits).
Now my question is: When does the HDD firmware determine a sector should be replaced. Users can know the development of sector replacement count from S.M.A.R.T item called "reallocated sector count".Ī sample HDD drive with too many reallocated sectors(the index 133 drops below threshold 140): This mechanism eliminates the need for OS to do bad sector managment itself.
As we all know, modern hard disk drives do internal bad sector management inside their firmware, that is, when the drive detects a physically damanged or unreliable physical sector, it replaces the bad one with a good one from the reserved sector store.
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