User's Manual

3 – Planning
Performance
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3.3
Performance
The SANbox2-8c switch supports class 2 and class 3 Fibre Channel service at
transmission rates of 1-Gbps or 2-Gbps with a maximum frame size of 2148
bytes. A port can transmit or receive at 1-Gbps or 2-Gbps depending on the
device to which it is connected. The port discovers the transmission speed prior to
login when the connected device powers up. Related performance characteristics
include the following:
 Distance
 Bandwidth
 Latency
3.3.1
Distance
Consider the physical distribution of devices and switches in the fabric. Choose
SFP transceivers that are compatible with the cable type, distance, Fibre Channel
revision level, and the device host bus adapter. Refer to
Appendix A Specifications for more information about cable types and SFP
transceivers.
Each port is supported by a data buffer with a 12 credit capacity; that is, 12
maximum sized frames. For fibre optic cables, this enables full bandwidth over a
distance of 20 kilometers at 1-Gbps (0.6 credits/Km), or 10 kilometers at 2-Gbps
(1.2 credits/Km). Beyond this distance, however, there is some loss of efficiency
because the transmitting port must wait for an acknowledgement before sending
the next frame.
Longer distances can be spanned at full bandwidth by extending credits on
G_Ports and F_Ports. Each port can donate 11 credits to a pool from which a
recipient port can borrow. For example, you can configure a recipient port to
borrow up to 66 credits from 6 ports for a total of 78 credits. This will support
communication over approximately 130 Km at 1 Gbps (78÷0.6) or 65 Km at 2
Gbps (78÷1.2).
You can configure recipient and donor ports using SANsurfer Switch Manager or
the Set Config command. Refer to ”Set Config Command” on page B-33 for more
information.