Chapter 11. Advanced Copy Services 497
Depending on the grain size of the FlashCopy mapping, the memory capacity usage is 
different. One MiB of memory provides the following volume capacity for the specified I/O 
group:
/SM590000For clones and snapshots FlashCopy with 256 KiB grains size, 2 TiB of total FlashCopy 
source volume capacity
/SM590000For clones and snapshots FlashCopy with 64 KiB grains size, 512 GiB of total FlashCopy 
source volume capacity
/SM590000For incremental FlashCopy, with 256 KiB grains size, 1 TiB of total incremental FlashCopy 
source volume capacity
/SM590000For incremental FlashCopy, with 64 KiB grains size, 256 GiB of total incremental 
FlashCopy source volume capacity
Review Table 11-9 to calculate the memory requirements and confirm that your system is 
able to accommodate the total installation size.
Table 11-9   Memory allocation for FlashCopy services
FlashCopy includes the FlashCopy function, Global Mirror with change volumes, and 
active-active (HyperSwap) relationships.
For multiple FlashCopy targets, you must consider the number of mappings. For example, for 
a mapping with a grain size of 256 KiB, 8 KiB of memory allows one mapping between a 
16 GiB source volume and a 16 GiB target volume. Alternatively, for a mapping with a 256 KiB 
grain size, 8 KiB of memory allows two mappings between one 8 GiB source volume and two 
8 GiB target volumes.
When creating a FlashCopy mapping, if you specify an I/O group other than the I/O group of 
the source volume, the memory accounting goes toward the specified I/O group, not toward 
the I/O group of the source volume.
When creating FlashCopy relationships or mirrored volumes, more bitmap space is allocated 
automatically by the system, if required.
For FlashCopy mappings, only one I/O group consumes bitmap space. By default, the I/O 
group of the source volume is used.
When you create a reverse mapping, such as when you run a restore operation from a 
snapshot to its source volume, a bitmap is created.
When you configure change volumes for use with Global Mirror, two internal FlashCopy 
mappings are created for each change volume.
Minimum allocated 
bitmap space
Default allocated 
bitmap space
Maximum allocated 
bitmap space
Minimum1 
functionality when 
using the default 
values
0 20 MiB 2 GiB 10 TiB of FlashCopy 
source volume 
capacity
5 TiB of incremental 
FlashCopy source 
volume capacity
1The actual amount of functionality might increase based on settings, such as grain size and strip 
size.