HP Brocade BladeSystem 4/24 Brocade Network Advisor SAN User Manual v11.1x (53 - Page 681

Adaptive Rate Limiting 20 • Circuits 0 and 1 are created with a metric of 0. Circuit 0 is created with a maximum transmission rate of 1 Gbps, and Circuit 1 is created with a maximum transmission rate of 500 Mbps. Together, Circuits 0 and 1 provide an available bandwidth of 1.5 Gbps. • Circuits 2 and 3 are created with a metric of 1. Both are created with a maximum transmission rate of 1 Gbps, for a total of 2 Gbps. This bandwidth is held in reserve. • If either circuit 0 or circuit 1 fails, traffic flows over the remaining circuit while the failed circuit is being recovered. The available bandwidth is still considered to be 1.5 Gbps. • If both circuit 0 and circuit 1 fail, there is a failover to circuits 2 and 3, and the available bandwidth is updated as 2 Gbps. • If a low metric circuit becomes available again, the high metric circuits go back to standby status, and the available bandwidth is updated again. For example, if circuit 0 is recovered, the available bandwidth is updated as 1 Gbps. If circuit 1 is also recovered, the available bandwidth is updated as 1.5 Gbps. Adaptive Rate Limiting Adaptive Rate Limiting (ARL) is performed on FCIP tunnel connections to change the rate in which the FCIP tunnel transmits data through the TCP connections. This feature is available only on the 8 Gbps extension switches and 8 Gbps Extension Blades. ARL uses information from the TCP connections to determine and adjust the rate limit for the FCIP tunnel dynamically. This allows FCIP connections to utilize the maximum available bandwidth while providing a minimum bandwidth guarantee. ARL applies a minimum and maximum traffic rate, and allows the traffic demand and WAN connection quality to dynamically determine the rate. As traffic increases, the rate grows towards the maximum rate, and if traffic subsides, the rate reduces towards the minimum. If traffic is flowing error-free over the WAN, the rate grows towards the maximum rate. If TCP reports an increase in retransmissions, the rate reduces towards the minimum. FSPF link cost calculation when ARL is used Fabric Shortest Path First (FSPF) is a link state path selection protocol that directs traffic along the shortest path between the source and destination based upon the link cost. When ARL is used, The link cost is equal to the sum of maximum traffic rates of all established, currently active low metric circuits in the tunnel. The following formulas are used: • If the bandwidth is greater than or equal to 2 Gbps, the link cost is 500. • If the bandwidth is less than 2 Gbps, but greater than or equal to 1 Gbps, the link cost is 1000000 divided by the bandwidth. • If the bandwidth is less than 1 Gbps, the link cost is 2000 minus the bandwidth QoS SID/DID priorities over an FCIP trunk QoS SID/DID traffic prioritization is a capability of Fabric OS Adaptive Networking licensed feature. This feature allows you to prioritize FC traffic flows between hosts and targets. Four internal TCP connections provide internal circuits for managing QoS SID/DID priorities over an FCIP tunnel, as illustrated in Figure 285. The priorities are as follows: Document Title 637 xx-xxxxxxx-01