FlashCopy indirection layer Read from the source Volume Write on the source Volume The FlashCopy indirection layer governs the I/O to the source and target volumes when a  FlashCopy mapping is started, which is done by using the FlashCopy bitmap. The purpose of  the FlashCopy indirection layer is to enable the source and target volumes for read and write  I/O immediately after the FlashCopy is started. The indirection Layer intercepts any I/O coming from a host (read or write operation) and  addressed to a FlashCopy volume (source or target). It determines whether the addressed  volume is a source or a target, its direction (read or write), and the state of the bitmap table for  the FlashCopy mapping that the addressed volume is in. It then decides what operation to  perform. The different I/O indirections are described next. When a user performs a read operation on the source volume, there is no redirection. The  operation is similar to what is done with a volume that is not part of a FlashCopy mapping. Performing a write operation on the source volume modifies a block or a set of blocks, which  modifies a grain on the source. It generates one of the following actions, depending on the  state of the grain to be modified. Consider the following points: GLYPH<SM590000> If the bitmap indicates that the grain was copied, the source grain is changed and the  target volume and the bitmap table remain unchanged, as shown in Figure 11-5. Figure 11-5 Modifying an already copied grain on the Source 468  Implementing the IBM System Storage SAN Volume Controller with IBM Spectrum Virtualize V8.2.1