If a hard disk drive (HDD) fails, the Oracle FS System uses the parity and the mirroring features of RAID technology, along with the dynamic spares, to ensure that data is not lost.
HDD arrays are configured with dynamic spares. In a RAID configuration, an HDD failure triggers a rebuild operation. During a rebuild operation, the reconstructed data is built on the spare HDD that is within the rebuilt stripe. When the failed HDD is replaced, the data held in the spare HDD is copied back to the replacement HDD.