The DiskDriveExtents are used with a failed realization.
The DiskDriveExtents used to replace a DiskDriveExtent whose realization fails are associated to the RedundancySet that uses an IsSpare association, as shown in IsSpare association.
Figure 1. IsSpare association
Class IBMTSSVC_IsSpare represents the association between the IBMTSSVC_DiskDriveExtent to be used as spares and the IBMTSSVC_StorageRedundancySet.