FlashCopy volume capacity per  I/O Group 4 pebibytes  (PiB) This maximum is a limit on the quantity of  FlashCopy mappings that are using bitmap space  from this I/O Group. This maximum configuration  uses all 4 gibibytes (GiB) of bitmap space for the  I/O Group and allows no Metro or Global Mirror  bitmap space. The default is 40 tebibytes (TiB). FlashCopy mappings per  Consistency Group 512 This limit is because of the time that is taken to  prepare a Consistency Group with many  mappings. FlashCopy property Maximum Comment 10.3.4 FlashCopy indirection layer 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 a 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. To show how the FlashCopy indirection layer works, we examine what happens when a  FlashCopy mapping is prepared and then started. When a FlashCopy mapping is prepared and started, the following sequence is applied: 1. Flush the write cache to the source volume or volumes that are part of a Consistency  Group. 2. Put cache into write-through mode on the source volumes. 3. Discard cache for the target volumes. 4. Establish a sync point on all of the source volumes in the Consistency Group (which  creates the FlashCopy bitmap). 5. Ensure that the indirection layer governs all of the I/O to the source volumes and target  volumes. 6. Enable cache on the source volumes and target volumes. GLYPH<SM590000> The volume and the logical block address (LBA) to which the I/O is addressed GLYPH<SM590000> Its direction (read or write) GLYPH<SM590000> The state of an internal data structure, the FlashCopy bitmap FlashCopy provides the semantics of a point-in-time copy by using the indirection layer, which  intercepts I/O that is directed at the source or target volumes. The act of starting a FlashCopy  mapping causes this indirection layer to become active in the I/O path, which occurs  automatically across all FlashCopy mappings in the Consistency Group.  The indirection layer then determines how each I/O is to be routed, based on the following  factors: The indirection layer allows the I/O to go through to the underlying volume, redirects the I/O  from the target volume to the source volume, or queues the I/O while it arranges for data to be  copied from the source volume to the target volume. To explain in more detail which action is  applied for each I/O, we first look at the FlashCopy bitmap. 476  Implementing the IBM Storwize V5000 Gen2 with IBM Spectrum Virtualize V8.2.1