Dell Force10 Z9000 FTOS Configuration Guide for Z9000 System - Page 300

www.dell.com | support.dell.com Buffer tuning Buffer Tuning allows you to modify the way your switch allocates buffers from its available memory, and helps prevent packet drops during a temporary burst of traffic. The S-Series ASICs implement the key functions of queuing, feature lookups, and forwarding lookups in hardware. • Forwarding Processor (FP) ASICs provide Ethernet MAC functions, queueing and buffering, as well as store feature and forwarding tables for hardware-based lookup and forwarding decisions. 1G and 10G interfaces use different FPs. Table 12-5 describes the type and number of ASICs per platform. Table 12-5. ASICS by Platform Hardware FP S50N, S50V 2 S25V, S25P, S25N 1 CSF 0 0 You can tune buffers at three locations, as shown in Figure 12-10. 1. CSF - Output queues going from the CSF. 2. FP Uplink-Output queues going from the FP to the CSF IDP links. 3. Front-End Link-Output queues going from the FP to the front-end PHY. All ports support eight queues, 4 for data traffic and 4 for control traffic. All 8 queues are tunable. Physical memory is organized into cells of 128 bytes. The cells are organized into two buffer pools- dedicated buffer and dynamic buffer. • Dedicated buffer is reserved memory that cannot be used by other interfaces on the same ASIC or by other queues on the same interface. This buffer is always allocated, and no dynamic recarving takes place based on changes in interface status. Dedicated buffers introduce a trade-off. They provide each interface with a guaranteed minimum buffer to prevent an overused and congested interface from starving all other interfaces. However, this minimum guarantee means the buffer manager does not reallocate the buffer to an adjacent congested interface, which means that in some cases, memory is underused. • Dynamic buffer is shared memory that is allocated as needed, up to a configured limit. Using dynamic buffers provides the benefit of statistical buffer sharing. An interface requests dynamic buffers when its dedicated buffer pool is exhausted. The buffer manager grants the request based on three conditions: • The number of used and available dynamic buffers • The maximum number of cells that an interface can occupy • Available packet pointers (2k per interface). Each packet is managed in the buffer using a unique packet pointer. Thus, each interface can manage up to 2k packets. 300 | Z-Series Debugging and Diagnostics