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