## 5.3.4 Global Mirror 

Global Mirror is a two-site, long distance, asynchronous, remote copy technology. This solution integrates the Global Copy and FlashCopy technologies. With Global Mirror, the data that the host writes at the local site is asynchronously mirrored to the storage unit at the remote site. With special management steps (under control of the local master storage unit), a consistent copy of the data is automatically maintained and periodically updated by using FlashCopy on the storage unit at the remote site. 

You need extra storage at the remote site for these FlashCopies. However, you can define your FlashCopy targets as Extent Space Efficient ESE volumes in an extent pool using small extents. 

The Global Mirror Journal volumes are a key use case for ESE to reduce the additional space that is required for this configuration. 

Global Mirror performs automatic space releases on such space-efficient Journal targets. This process will not occur on every consistency group formation, but often and in a regular manner. 

Global Mirror features the following benefits: 

GLYPH<SM590000> Support for almost unlimited distances between the local and remote sites, with the distance typically limited only by the capabilities of the network and the channel extension technology. You can use this unlimited distance to choose your remote site location based on business needs. This capability enables site separation to add protection from globalized disasters. 

GLYPH<SM590000> A consistent and restartable copy of the data at the remote site, which is created with minimal impact to applications at the local site. 

GLYPH<SM590000> Data currency where, for many environments, the remote site lags behind the local site typically 3 - 5 seconds, which minimizes the amount of data exposure if an unplanned outage occurs. The actual lag in data currency that you experience depends on many factors, including specific workload characteristics and bandwidth between the local and remote sites. 

GLYPH<SM590000> Dynamic selection of the Recovery Point Objective (RPO) that you want, based on business requirements and optimization of available bandwidth. 

GLYPH<SM590000> Session support in which data consistency at the remote site is internally managed across up to eight storage units that are at the local site and the remote site. 

GLYPH<SM590000> Efficient synchronization of the local and remote sites with support for failover and failback operations. This configuration helps to reduce the time that is required to switch back to the local site after a planned or unplanned outage. 

