526 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
Global Mirror write I/O from production system to a secondary system requires serialization 
and sequence-tagging before being sent across the network to a remote site (to maintain a 
write-order consistent copy of data). 
To avoid affecting the production site, IBM Spectrum Virtualize supports more parallelism in 
processing and managing Global Mirror writes on the secondary system by using the 
following methods:
/SM590000Secondary system nodes store replication writes in new redundant non-volatile cache
/SM590000Cache content details are shared between nodes
/SM590000Cache content details are batched together to make node-to-node latency less of an issue
/SM590000Nodes intelligently apply these batches in parallel as soon as possible
/SM590000Nodes internally manage and optimize Global Mirror secondary write I/O processing
In a failover scenario where the secondary site must become the master source of data, 
certain updates might be missing at the secondary site. Therefore, any applications that use 
this data must have an external mechanism for recovering the missing updates and 
reapplying them, such as a transaction log replay.
Global Mirror is supported over FC, FC over IP (FCIP), FC over Ethernet (FCoE), and native 
IP connections. The maximum distance cannot exceed 80 ms round trip, which is about 
4000 km (2485.48 miles) between mirrored systems. However, starting with IBM Spectrum 
Virtualize V7.4, this distance was significantly increased for certain IBM Storwize Gen2 and 
IBM SAN Volume Controller configurations. Figure 11-90 shows the current supported 
distances for Global Mirror remote copy.
Figure 11-90   Supported Global Mirror distances
11.6.12  Global Mirror features
IBM Spectrum Virtualize Global Mirror supports the following features: 
/SM590000Asynchronous remote copy of volumes that are dispersed over metropolitan-scale 
distances.
/SM590000IBM Spectrum Virtualize implements the Global Mirror relationship between a volume pair, 
with each volume in the pair being managed by an IBM Spectrum Virtualize system.
/SM590000IBM Spectrum Virtualize supports intracluster Global Mirror where both volumes belong to 
the same system (and I/O Group).
/SM590000An IBM Spectrum Virtualize system can be configured for partnership with 1 - 3 other 
systems. For more information about IP partnership restrictions, see 11.8.2, “IP 
partnership limitations” on page 550.
/SM590000Intercluster and intracluster Global Mirror can be used concurrently, but not for the 
same volume.