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: Because FlashCopy target volumes are immediately accessible in Read and Write mode, it is  possible to perform write operations on the target volume when the FlashCopy mapping is  started.  Write on a Target Volume Write on the source Volume Read from the source Volume 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. GLYPH<SM590000> If the bitmap indicates that the grain was not yet copied, the grain is first copied on the  target (copy on write), the bitmap table is updated, and the grain is modified on the source,  as shown in Figure 11-6. Figure 11-5 Modifying an already copied grain on the Source Figure 11-6 Modifying a non-copied grain on the source 444  Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1