Buffer credits, Basic port configuration – Brocade Communications Systems 415 User Manual
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Brocade Adapters Administrator’s Guide
53-1001583-01
Buffer credits
3
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.
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
Yes
Configure speed
Yes
Yes
Frame data field size
Yes
Yes
Persistent Binding
Note: The persistent binding option is
available on Windows platforms only.
Yes
Yes
QoS
Yes
Yes
Path Time Out
Note: Path time out value (pathtov) is
valid for firmware versions 2.0 and
higher. It is not supported on the
Solaris operating system.
Yes
Yes
Target Rate Limiting
Yes
Yes