sentences:  Because the reliability of the system depends on quick replacement of the bad drive so the array can rebuild, it is common to include hot spares that can immediately start rebuilding the array upon failure.However, this does not address the issue that the array is put under maximum strain reading every bit to rebuild the array at the time when it is most vulnerable.RAID 50 improves upon the performance of RAID 5 particularly during writes, and provides better fault tolerance than a single RAID level does.