How Data ONTAP works with hot spare disks

Cluster-Mode System Manager Help : Cluster-Mode : Cluster > Storage > Aggregates : Understanding aggregates : How Data ONTAP works with hot spare disks

A hot spare disk is a disk that is assigned to a storage system but is not in use by a RAID group. It does not yet hold data but is ready for use. If a disk failure occurs within a RAID group, Data ONTAP automatically assigns hot spare disks to RAID groups to replace the failed disks.