10.8 Consistency protection for Remote and Global mirror Before V7.8.1, Metro Mirror and regular Global Mirror relationships and consistency groups  stop when one of the following events occurs: Consistency of the secondary volume is lost during resynchronization, so the relationship is  automatically stopped and a 1720 error is raised, which requires the user to restart the  relationship manually. Global Mirror with Change Volumes (GMCV) relationships use a secondary change volume to  retain a consistent copy during resync and automatically restart when they can. From V7.8.1, Metro Mirror and regular Global Mirror also behave like GMCV relationship if a  secondary change volume is configured which does the following: The consistency protection mechanism for Metro Mirror and regular Global Mirror uses  change volumes and has following characteristics: Consistency protection for Metro or regular Global Mirror can be enabled by configuring a  secondary change volume and no further configuration is needed to enable this behavior. All  relationships in a consistency group must be so configured for this behavior to work on any  relationship in the consistency group. Table 10-11 lists the events and the expected behavior when consistency protection  mechanism is enabled for metro mirror and regular global mirror. 558  Implementing the IBM Storwize V5000 Gen2 with IBM Spectrum Virtualize V8.2.1 Table 10-11 Events and expected behavior Event Expected behavior for the relationship Link down or secondary volume offline Relationship is  consistent_synchronized ( started  and  in sync ) GLYPH<SM590000> Retain the secondary consistent copy GLYPH<SM590000> Prepare for resynchronization  GLYPH<SM590000> Go to the  consistent_copying  state GLYPH<SM590000> Automatically resume replication as and when  possible  GLYPH<SM590000> Return to  consistent_synchronized  when  complete GLYPH<SM590000> Requires both participating systems to be at V7.8.1 or later GLYPH<SM590000> Supported on all systems that can have remote mirroring license GLYPH<SM590000> Uses two FlashCopy maps per relationship per system (so maximum of 2500 relationships  on a 10k volume-capable system) GLYPH<SM590000> Does not need FlashCopy license  GLYPH<SM590000> It is a tweak to Metro Mirror and Global Mirror copy types by using technology that is in  Global Mirror with Change Volumes GLYPH<SM590000> Stop as before if no secondary change volume configured GLYPH<SM590000> Makes Metro Mirror and Global Mirror more suited to links with intermittent connectivity  and IP replication GLYPH<SM590000> A secondary volume goes offline GLYPH<SM590000> The link between systems goes down