Buffer credits, Basic port configuration – Brocade Communications Systems 415 User Manual

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Brocade Adapters Administrator’s Guide

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Buffer credits

Buffer-to-buffer credit flow control is implemented to limit the amount of data a port sends, based
on the number and size of the frames sent from that port. This scheme allows Fibre Channel to be
self-throttling, thereby allowing it to establish a reliable connection without the need to
accommodate dropped frames due to congestion. Buffer credit limits between each device and the
fabric are communicated at the time of fabric login. One buffer credit allows a device to send one
frame of data (typically 1 or 2 KB). Buffer credits cannot be configured on an adapter.

The default BB Credit is 1. The baseline for the calculation is one credit per kilometer at 2 Gbps.
This yields the following values for 10 km:

•

5 credits per port at 1 Gbps

•

10 credits per port at 2 Gbps

•

20 credits per port at 4 Gbps

•

40 credits per port at 8 Gbps

Refer to the “Extended Fabrics concepts and planning” section of the Fabric OS Administrator’s
Guide for detailed information about buffer credits.

Basic port configuration

For each port, you can configure the following parameters using the Basic Port Configuration dialog
box, the Brocade Command Line utility (BCU), or both.

Table 6

lists the features and configuration

options.

TABLE 6

Basic port configuration options

Port configuration parameter

Configurable using
HCM

Configurable using
the BCU

For more information

Port logging level

Yes

“Port logging level”