24 Brocade Adapters Administrator’s Guide
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Buffer credits
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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 7 lists the features and configuration
options.
TABLE 7 Basic port configuration options
Port configuration parameter
Configurable using
the GUI
Configurable using
the BCU For more information
Port logging level1Yes Yes “Port logging level”
Configure speed (HBA only) Yes Yes “Port speed”
Frame data field size Yes Yes “Frame data field size”
Persistent Binding
Note: The persistent binding option is
available on Windows platforms only.
Yes Yes “Persistent binding”
QoS (HBA only) Yes Yes “QoS (HBA only)”
MPIO mode (HBA only) Yes Yes “MPIO (HBA only)”
Path Time Out 2 Yes Yes “Path Time Out”
Target Rate Limiting (HBA only) Yes Yes “Target rate limiting (HBA only)”
Boot over SAN (HBA only) Yes Yes “Boot over SAN (HBA only)”
Boot code image upload (HBA only) Yes Yes “Boot code image upload (HBA
only)”
1 If an Ethernet port is selected, the Basic Port Configuration dialog displays an additional feature called
“Eth Logging Level.”
2 Path Time Out is available only when MPIO is disabled.