McDATA 4416 manual Bandwidth, Latency

Performance

Bandwidth

Bandwidth is a measure of the volume of data that can be transmitted at a given transmission rate. A Fibre Channel port can transmit or receive at nominal rates of 1-Gbps, 2-Gbps, or 4-Gbps depending on the device to which it is connected. This corresponds to actual bandwidth values of

106 MB, 212 MB, and 425 MB respectively. Multiple source ports can transmit to the same destination port if the destination bandwidth is greater than or equal to the combined source bandwidth. For example, two 1-Gbps source ports can transmit to one 2-Gbps destination port. Similarly, one source port can feed multiple destination ports if the combined destination bandwidth is greater than or equal to the source bandwidth.

In multiple chassis fabrics, each link between chassis contributes 106, 212, or 425 MB of bandwidth between those chassis depending on the speed of the link. When additional bandwidth is needed between devices, increase the number of links between the connecting switches. The switch module guarantees in-order-delivery with any number of links between chassis.

Latency

Latency is a measure of how fast a frame travels from one port to another. The factors that affect latency include transmission rate and the source/destination port relationship as shown in Table 2-2.

Table 2-2. Port-to-Port Latency

	Destination Rate
	Gbps	1	2		4
	1	< 0.6 µsec	< 0.8	µsec1	< 0.8	µsec1
Rate
	2	< 0.5 µsec	< 0.4	µsec	< 0.4	µsec1
Source
	4	< 0.4 µsec	< 0.3	µsec	< 0.3	µsec

1Based on minimum frame size of 36 bytes. Latency increases for larger frame sizes.

Planning

2-5