830 | Quality of Service (QoS)w w w . d e l l . c o m | s u p p o r t . d e l l . c o m Allocate bandwidth to queueThe E-Series schedules unicast, multicast, and replication traffic for egress based on the Weighted FairQueuing algorithm. The C-Series and S-Series schedule packets for egress based on Deficit Round Robin(DRR). These strategies both offer a guaranteed data rate.To allocate bandwidth to queues on the C-Series and S-Series, assign each queue a weight ranging from 1to 1024, in increments of 2 n, using the command bandwidth-weight. Table 39-3 shows the defaultbandwidth weights for each queue, and their equivalent percentage which is derived by dividing thebandwidth weight by the sum of all queue weights.The key difference between allocating bandwidth by weight on the C-Series and S-Series and allocatingbandwidth by percentage on the E-Series because you are required to choose a bandwidth weight inincrements of 2 n you may not be able to achieve exactly a target bandwidth allocation.A key similarity between allocating bandwidth by percentage and allocating by weight is that assigning aweight or percentage to one queue affects the amount of bandwidth that is allocated to other queues.Therefore, whenever you are allocating bandwidth to one queue, Dell Force10 recommends that youevaluate your bandwidth requirements for all other queues as well.Table 39-4 shows an example of choosing bandwidth weights for all four queues to achieve a targetbandwidth allocation.Note: Dell Force10 recommends assigning bandwidth to all queues. If queues are left un-allocated, theremaining bandwidth is shared equally among the un-allocated queues. If the sum of the allocatedbandwidth percentage exceeds 100% 1% from the allocated queues will be assigned to each un-allocatedqueues.Table 39-3. Default Bandwidth Weights for C-Series and S-SeriesQueue Default WeightEquivalentPercentage0 1 6.67%1 2 13.33%2 4 26.67%3 8 53.33%Table 39-4. Assigning Bandwidth Weights for the C-Series and S-SeriesQueue WeightEquivalentPercentageTargetAllocation0 1 0.44% 1%1 64 28.44% 25%2 128 56.89% 60%3 32 14.22% 14%
