IP SANs: A Guide to iSCSI, iFCP, and FCIP Protocols for Storage Area Networks

11.1. Class of Service and QoS

Without a means of setting data delivery policies, all data within a network infrastructure receives equal treatment. A download of an inconsequential but large graphics file would get the same priority as an on-line transaction processing an update of a critical customer order. Even in the absence of mixed traffic in a shared network, some applications require more strict enforcement of data delivery. In Fibre Channel SANs, for example, the vast majority of applications are run over fabrics using connectionless class 3 service. Class 3 provides best-effort delivery and no acknowledgment of data receipt. The next higher lever of service is class 2, which provides acknowledgment, and above class 2 there is class ...