598 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
For every Remote Copy relationship that is created on an IBM Spectrum Virtualize system, a 
bitmap table is created to track the copied grains. By default, the system allocates 20 MiB of 
memory for a minimum of 2 TiB of remote copied source volume capacity. 
Every 1 MiB of memory provides volume capacity for the specified I/O group. So, for 256 KiB 
grains size, 2 TiB of total Metro Mirror, Global Mirror, or active-active volume capacity is 
provided.
See Table 11-14 to calculate the memory requirements and confirm that your system is able 
to accommodate the total installation size.
Table 11-14   Memory allocation for FlashCopy services
When you configure change volumes for use with Global Mirror, two internal FlashCopy 
mappings are created for each change volume.
For Metro Mirror, Global Mirror, and HyperSwap active-active relationships, two bitmaps exist. 
For MM/GM relationships, one is used for the master clustered system and one is used for the 
auxiliary system because the direction of the relationship can be reversed. For active-active 
relationships, which are configured automatically when HyperSwap volumes are created, one 
bitmap is used for the volume copy on each site because the direction of these relationships 
can be reversed. 
MM/GM relationships do not automatically increase the available bitmap space. You might 
need to use the chiogrp command to manually increase the space in one or both of the 
master and auxiliary systems.
You can modify the resource allocation for each I/O group of an IBM SAN Volume Controller 
system by opening the Settings → System panel and clicking the Resources menu, as 
shown in Figure 11-154.
Figure 11-154   Modifying resources allocation
Minimum allocated 
bitmap space
Default allocated 
bitmap space
Maximum allocated 
bitmap space
Minimum 
functionality when 
using the default 
values1
0 20 MiB 512 MiB 40 TiB of remote 
mirroring volume 
capacity
1Remote copy includes Metro Mirror, Global Mirror, and active-active relationships.