Target writes with Multiple Target FlashCopy A write to an intermediate or newest target volume must consider the state of the grain within  its own mapping, and the state of the grain of the next oldest mapping: If the grain being read has already been copied from the source to the target, the read simply  returns data from the target being read. If the grain has not been copied, each of the newer  mappings is examined in turn and the read is performed from the first copy found. If none are  found, the read is performed from the source.  The FlashCopy function, like all the advanced IBM Spectrum Virtualize and Storwize family  product features, offers useful capabilities. However, some basic planning considerations are  to be followed for a successful implementation. To plan for and implement FlashCopy, you must check the configuration limits and adhere to  them. Table 5-3 shows the system limits that apply to the latest version at the time of writing  this book. Configuration Limits:  The configuration limits always change with the introduction of new  hardware and software capabilities. Check the IBM Spectrum Virtualize/Storwize online  documentation for the latest configuration limits. GLYPH<SM590000> If the grain of the next oldest mapping has not been copied yet, it must be copied before  the write is allowed to proceed to preserve the contents of the next oldest mapping. The  data that is written to the next oldest mapping comes from a target or source. GLYPH<SM590000> If the grain in the target being written has not yet been copied, the grain is copied from the  oldest already copied grain in the mappings that are newer than the target, or the source if  none are already copied. After this copy is done, the write can be applied to the target. Target reads with Multiple Target FlashCopy 5.2.4 FlashCopy planning considerations FlashCopy configurations limits Table 5-3 FlashCopy properties and maximum configurations 192  IBM System Storage SAN Volume Controller, IBM Storwize V7000, and IBM FlashSystem 7200 Best  FlashCopy property Maximum Comment FlashCopy targets per source 256 This maximum is the maximum number of  FlashCopy mappings that can exist with the same  source volume. FlashCopy mappings per system 5000 This maximum is the maximum number of  FlashCopy mappings per system FlashCopy Consistency Groups  per system 500 This maximum is an arbitrary limit that is policed  by the software. FlashCopy volume space per I/O  Group 4096 TB This maximum is a limit on the quantity of  FlashCopy mappings by using bitmap space from  one I/O Group.  FlashCopy mappings per  Consistency Group 512 This limit is due to the time that is taken to prepare  a Consistency Group with many mappings.