Q: Which is better for storage traffic in Ethernet networks — Policing or Shaping?
Neither. Both limit traffic rates, although slightly differently. Policing drops excess traffic, which results in retransmitting the lost packets or re-initiating the entire operation based on the upper layers. In contrast, shaping leads to buffering a limited amount of excess traffic, which increases delay and variance in delay, and still drops excess traffic. Both lead to poor performance for storage traffic. 都不是。两者都限制流量速率，但略有不同。极化会丢弃多余的流量，导致重新传输丢失的数据包或根据上层重新启动整个操作。与此相反，整形会导致缓冲有限的过量流量，从而增加延迟和延迟差异，但仍会丢弃过量流量。这两种方法都会导致存储流量性能低下。
The aim should be to have enough network capacity such that neither policing nor shaping is needed. 目标应该是拥有足够的网络容量，从而既不需要监控，也不需要整形。
Q: What is the difference between Priority and Bandwidth in the context of QoS?
While using multiple egress queues on a network port, packets are sent from the priority queue before the packets from other queues. This scheme works great for delay-sensitive traffic, but it can starve traffic in other queues. To avoid this issue, a priority queue is assigned a maximum bandwidth limit, such as 20% of the link capacity. 在网络端口上使用多个出口队列时，优先队列的数据包会先于其他队列的数据包发送。这种方案对延迟敏感的流量非常有效，但会使其他队列的流量处于饥饿状态。为避免这一问题，优先队列会被分配一个最大带宽限制，例如链路容量的 20%。
Other queues are assigned a minimum bandwidth guarantee, such as 80% of the link capacity, but this is not a maximum limit. 其他队列被分配了最低带宽保证，如链路容量的 80%，但这不是最大限制。
The important point to remember is that these limits are enforced only in the presence of other traffic (under congestion). When there is no traffic in the priority queue, the other queue can consume up to 100% capacity. Likewise, when there is no traffic in another queue, the priority queue can consume up to 100% capacity. When there is traffic in both queues, 20% of traffic in the priority queue is transmitted with low delay, but its bandwidth is limited to 20%. The 80% of traffic in other queues is transmitted with relatively higher delay, but it gets at least 80% capacity. 需要记住的重要一点是，只有在有其他流量的情况下（拥堵时）才会执行这些限制。当优先队列中没有流量时，其他队列最多可占用 100%的容量。同样，当另一个队列中没有流量时，优先队列也可以占用 100% 的容量。当两个队列都有流量时，优先队列中 20% 的流量会以低延迟传输，但其带宽仅限于 20%。其他队列中 80% 的流量传输延迟相对较高，但至少能获得 80% 的容量。
Summary
This chapter briefly explains the types of storage, storage protocols, their transports, and networks in a data center. Even experienced users may be overwhelmed by all these options. However, for the scope of this book, just remember that the details of the protocol stack are abstracted by the end devices before sending packets on the networks