Intersite link planning

Specific intersite link requirements must be met when you are planning to use IP partnership for remote copy.

If you use IP partnership, you must meet the following requirements:
  • TCP ports 3260 and 3265 are used by systems for IP partnership communications; therefore, these ports need to be open.
  • The maximum supported round-trip time between systems is 80 milliseconds (ms) for a 1 Gbps link.
  • The maximum supported round-trip time between systems is 10 milliseconds (ms) for a 10 Gbps link.
  • For IP partnerships, the recommended method of copying is by using Global Mirror with change volumes because of the performance benefits. Also, Global Mirror and Metro Mirror might be more susceptible to the loss of synchronization.
  • A 25 Gbps link is supported for IP replication. However, it offers no performance advantage over a dedicated 10 Gbps port.
  • IP partnerships can also support data compression. Both systems in the IP partnership must be running a software level that supports IP partnership data compression. Compression must also be functional on each system. For more information, see Configuring IP partnerships.
  • The amount of intersite heartbeat traffic is 1 megabit per second (Mbps) per link.
  • The minimum bandwidth requirement for the intersite link is 10 Mbps. However, this requirement scales up with the amount of host I/O that you choose to do. Figure 1 describes the scaling of host I/O.
    Figure 1. Scaling of host I/O
    Scaling of host I/O

    The equations that can describe the approximate minimum bandwidth that is required between two systems with < 5 ms round-trip time and errorless link follow.

    For systems that use Global Mirror or Metro Mirror:

    Minimum intersite link bandwidth in Mbps > Maximum(Minimum Link Bandwidth of 10Mbps , Required Background Copy in Mbps + Maximum Host I/O in Mbps + 1 Mbps heartbeat traffic)

    For systems that use only Global Mirror with change volumes:

    Minimum intersite link bandwidth in Mbps > Maximum(Minimum Link Bandwidth of 10Mbps , Required Background Copy in Mbps + 1 Mbps heartbeat traffic)

    Increasing latency and errors results in a higher requirement for minimum bandwidth.

Figure 2 shows how the IBM Spectrum Virtualize solution maintains near line-speed performance by masking the latency of the line. Even as the line latency increases, the performance of the technology enables the line to continue to exceed that of a plain link. The throughput limit is the uncompressed data rate, which is measured as the remote node send data rates. The round-trip time (RTT) is measured as the IP link RTT (pinging between the two nodes on the same ports that are being used for replication). The throughput limit is based on the distance and the uncompressed data rate.

Figure 2. Product transfer rate comparison for systems built with IBM Spectrum Virtualize
IBM Spectrum Virtualize transfer rate comparison