Dell PowerConnect Brocade 300 Fabric OS Administrator's Guide v7.1.0 - Page 565

Buffer credit management 23 TABLE 84 Configurable distances for Extended Fabrics (Continued) Maximum distances (km) that can be configured (assuming a 2112-byte frame size) Switch/blade model 2 Gbps 4 Gbps 8 Gbps 10 Gbps 16 Gbps FC8-32 FC8-32E FC8-48 FC8-48E FC8-64 FC16-32 FC16-48 FS8-18 FX8-24 1294 647 323 N/A N/A 5190 2595 1297 1038 648 1230 615 307 N/A N/A 4486 2243 1121 897 560 *** Extended Fabrics is not supported on this blade *** 5190 2595 1297 1038 648 4486 2243 1121 897 560 1604 802 401 N/A N/A 1062 531 265 N/A N/A NOTE The distances in this table assume that QoS is enabled. If QoS is disabled the maximum supported distances are higher, because QoS requires an additional 20 buffer credits per active port. To get an estimated maximum equally distributed distance for n number of ports at a particular speed X, divide the 1-port maximum distance of the switch at speed X by n. For example, for three ports running at 2 Gbps on a Brocade 300 switch, the maximum equally distributed distance is calculated as 486 / 3 = 164 km. Downgrade considerations When Fabric OS firmware is downgraded from version 7.1 to an earlier version, the effect depends on whether the number of buffer credits for the long-distance port is configured with the -framesize and -distance options or with the -buffers option. When a port is configured with -framesize and -distance options In Fabric OS v7.1, if you configure the port by using the -distance option alone, the reserved buffers are calculated according to the distance. If you configure both the -framesize option and the -distance option, more buffers will be reserved, depending on the frame size. With a firmware downgrade, those ports that were configured with more reserved buffers will keep the reserved buffers as long as the ports remain online. The next time the port is toggled, buffers will again be reserved on the basis of distance only. When a port is configured with the -buffers option A firmware downgrade is blocked when a port is configured as a long-distance port by means of the -buffers option. The following warning message is displayed: Downgrade to selected version is not allowed because few ports are configured with Longdistance -buffers option. Please remove the configuration using portcfglongdistance / L0 CLI or change the configuration with -distance option on the console. Fabric OS Administrator's Guide 565 53-1002745-02