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GLYPH<SM590000> The RC buffer size setting must be 512 MB on each system in the partnership. This setting can be accomplished by running the chsystem -rcbuffersize 512  command on each system. 

Important:  Changing this setting is disruptive to Metro Mirror and Global Mirror operations. Use this command only before partnerships are created between systems, or when all partnerships with the system are stopped. 

GLYPH<SM590000> Two Fibre Channel ports on each node that will be used for replication must be dedicated for replication traffic. This configuration can be achieved by using SAN zoning and port masking. 

GLYPH<SM590000> SAN zoning should be applied to provide separate intrasystem zones for each local-remote I/O group pair that is used for replication. See “Remote system ports and zoning considerations” on page 187 for further zoning guidelines. 

## Link bandwidth that is used by internode communication 

IBM Spectrum Virtualize uses part of the bandwidth for its internal intersystem heartbeat. The amount of traffic depends on how many nodes are in each of the local and remote systems. Table 6-7 shows the amount of traffic (in megabits per second) that is generated by different sizes of systems. 

<img src='content_image/982735.jpg'>

These numbers represent the total traffic between the two systems when no  I/O is occurring to a mirrored volume on the remote system. Half of the data is sent by one system, and half of the data is sent by the other system. The traffic is divided evenly over all available connections. Therefore, if you have two redundant links, half of this traffic is sent over each link during fault-free operation. 

If the link between the sites is configured with redundancy to tolerate single failures, size the link so that the bandwidth and latency statements continue to be accurate even during single failure conditions. 

## Network sizing considerations 

Proper network sizing is essential for the remote copy services operations. Failing to estimate the network sizing requirements can lead to poor performance in remote copy services and the production workload. 

Consider that intersystem bandwidth should be capable of supporting the combined traffic of the following items: 

GLYPH<SM590000> Mirrored foreground writes, as generated by your server applications at peak times 

GLYPH<SM590000> Background resynchronization, for example, after a link outage 

GLYPH<SM590000> Inter-system heartbeat 

