Brocade Communications Systems 804 Buffer credits, Basic port configuration, Configurable using

3 Buffer credits

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

	Configurable using	Configurable using
Port configuration parameter	HCM	the BCU	For more information
Port logging level	Yes	Yes	“Port logging level”
Configure speed	Yes	Yes	“Port speed”
Frame data field size	Yes	Yes	“Frame data field size”
Persistent Binding	Yes	Yes	“Persistent binding”
Note: The persistent binding option is
available on Windows platforms only.
QoS	Yes	Yes	“QoS”
Path Time Out	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.
Target Rate Limiting	Yes	Yes	“Target rate limiting”

20	Brocade Adapters Administrator’s Guide
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