Strategies for Data Protection - Brocade

Storage-Centric vs. Network-Centric SAN Architecturesmance backbone at the core. This tiered approach preserves theability to assign storage LUNs to any server, while facilitating expansionof the fabric to support additional storage capacity and serverconnections.For simplicity, the figures shown above do not detail alternate or dualpathing between servers, switches, and storage. The fabric illustratedin Figure 4, for example, could be the A side of a dual-path configuration.If directors are used, however, the full redundancy and 99.999percent availability characteristic of enterprise-class switches provideanother means to implement dual pathing. A server with dual HBAscould have one link connected to a director port on one blade, and aredundant link connected to a director port on a different blade. Likewise,storage connections can be provided from storage ports todifferent blades on the same director chassis. As in Fabric A and B,this configuration provides failover in the event of loss of an HBA, link,port, blade, or storage port.Inter-Fabric RoutingFibre Channel is a link layer (Layer 2) protocol. When two or more FibreChannel switches are connected to form a fabric, the switches engagein a fabric-building process to ensure that there are no duplicateaddresses in the flat network address space. The fabric shortest pathfirst (FSPF) protocol is used to define optimum paths between the fabricswitches. In addition, the switches exchange Simple Name Server(SNS) data, so that targets on one switch can be identified by initiatorsattached to other switches. Zoning is used to enforce segregation ofdevices, so that only authorized initiators can access designated targets.Analogous to bridged Ethernet LANs, a fabric is a subnet with asingle address space, which grows in population as more switches anddevices are added.At some point, however, a single flat network may encounter problemswith stability, performance, and manageability if the network grows toolarge. When a fabric reaches an optimum size, it is time to begin buildinga separate fabric instead of pushing a single fabric beyond itslimits. The concept of a manageable unit of SAN is a useful tool fordetermining the maximum number of switches and devices that willhave predictable behavior and performance and can be reasonablymaintained in a single fabric.Strategies for Data Protection 11