Bandwidth; Latency; Port-To-Port Latency - HP StorageWorks 8/20q Installation And Reference Manual

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 8 Gb/s, 4 Gb/s, or 2 Gb/s depending on the
device to which it is connected. This corresponds to full duplex bandwidth values of 1,700 MB, 850 MB,
and 424 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 4 Gb/s source
ports can transmit to one 8 Gb/s 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 switch fabrics, each link contributes up to 1,700 MB of bandwidth between those switches,
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 guarantees in-order delivery with any number
of links.

Latency

Latency is a measure of how fast a frame travels through a switch from one port to another. The factors that
affect latency include transmission rate and the source/destination port relationship
Table 6

Port-to-port latency

Destination Rate
Gbps
Source
2
Rate
4
8
1 Based on minimum frame size of 36 bytes. Latency increases for larger frame sizes.
2 4
< 0.6 μsec < 0.7 μsec
< 0.4 μsec < 0.3 μsec
< 0.3 μsec < 0.2 μsec
HP StorageWorks 8/20q Fibre Channel Switch Installation and Reference Guide
8
1 1
< 0.6 μsec
1
< 0.4 μsec
< 0.2 μsec
(Table 6).
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