Whats a hot spare?
A hot spare is a drive that is not used in a RAID set until a drive fails. When a drive fails, the hot spare replaces the failed drive. An enclosure that supports a Hot Spare feature can automatically sense when it’s time to use the new drive, and begin the recovery process even if no human is around to trigger it. If this should happen to you, simply replace the bad drive with a new drive, and the RAID array will be able to recover itself again if a drive goes bad.