658 | Debugging and Diagnosticsw w w . d e l l . c o m | s u p p o r t . d e l l . c o m Deciding to Tune BuffersDell Force10 recommends exercising caution when configuring any non-default buffer settings, as tuningcan significantly affect system performance. The default values work for most cases.As a guideline, consider tuning buffers if traffic is very bursty (and coming from several interfaces). In thiscase:• Reduce the dedicated buffer on all queues/interfaces.• Increase the dynamic buffer on all interfaces.• Increase the cell pointers on a queue that you are expecting will receive the largest number of packets.Buffer Tuning CommandsTo tune the buffers, use the following commands:Configuration changes take effect immediately and appear in the running configuration. Because undernormal conditions all ports do not require the maximum possible allocation, the configured dynamicallocations can exceed the actual amount of available memory; this is called oversubscription. If youchoose to oversubscribe the dynamic allocation, a burst of traffic on one interface might prevent otherinterfaces from receiving the configured dynamic allocation, which causes packet loss.You cannot allocate more than the available memory for the dedicated buffers. If the system determinesthat the sum of the configured dedicated buffers allocated to the queues is more than the total availablememory, the configuration is rejected, returning a syslog message similar to the following.Task Command Command ModeDefine a buffer profile for the FP queues. buffer-profile fp fsqueue CONFIGURATIONDefine a buffer profile for the CSF queues. buffer-profile csf csqueue CONFIGURATIONChange the dedicated buffers on a physical 1Ginterface.buffer dedicated BUFFER PROFILEChange the maximum amount of dynamic buffersan interface can request.buffer dynamic BUFFER PROFILEChange the number of packet-pointers per queue. buffer packet-pointers BUFFER PROFILEApply the buffer profile to a CSF to FP link. buffer csf linecard CONFIGURATIONFTOS Behavior: If you attempt to apply a buffer profile to a non-existent port-pipe, FTOS displays thefollowing message. However, the configuration still appears in the running-config.%DIFFSERV-2-DSA_BUFF_CARVING_INVALID_PORT_SET: Invalid FP port-set 2 for linecard 2. Validrange of port-set is <0-1>Table 39-3. Buffer Allocation Error00:04:20: %S50N:0 %DIFFSERV-2-DSA_DEVICE_BUFFER_UNAVAILABLE: Unable to allocate dedicated buffers forstack-unit 0, port pipe 0, egress port 25 due to unavailability of cells
