DRAID Rebuild DRAID copyback  Figure 2-8 DRAID copyback Chapter 2. IBM FlashSystem 9100 architecture  21 Figure 2-7 Physical capacity threshold DRAID copyback is a similar process to the rebuild process. Upon completion, FS9100  releases the space area by UNMAP-ing the area that was used, as shown in Figure 2-8. The spare area for rebuild on FS9100 is reserved against the physical capacity of the drives.  As the rebuild progresses, the data is copied to the remaining drives, increasing the capacity  threshold as shown in Figure 2-7. 