As the distance between two MetroCluster sites increases, latency increases, usually in the range of 1 ms round-trip delay time per 100 km (62 miles). Latency also depends on the network service level agreement (SLA) in terms of the bandwidth of the ISL links, packet drop rate, and jitter on the network. Low bandwidth, high jitter, and random packet drops lead to different recovery mechanisms by the switches, or the TCP engine on the controller modules, for successful packet delivery. These recovery mechanisms can increase overall latency. For specific information on round trip latency and maximum distance requirements for your configuration, refer to the Hardware Universe.

Any device that contributes to latency must be accounted for.

The Hardware Universe. provides the distance in km. You must allocate 1ms for every 100km. The maximum distance is defined by what is reached first, either the maximum round-trip time (RTT) in ms, or the distance in km. For example – if The Hardware Universe lists a distance of 300km, translating to 3ms, your ISL can be no further than 300km and the max RTT cannot exceed 3ms – whichever is reached first.

Packet loss must be less than, or equal to, 0.01%. The maximum packet loss is the sum of all loss on all links on the path between the MetroCluster nodes, and the loss on the local MetroCluster IP interfaces.

The supported jitter value is 3ms for round trip (or 1.5ms for one-way).

The network should allocate and maintain the SLA amount of bandwidth required for MetroCluster traffic, regardless of microbursts and spikes in the traffic.

If you are using ONTAP 9.7 or later, the intermediate network between the two sites must provide a minimum bandwidth of 4.5Gbps for the MetroCluster IP configuration.