Single-Tier Topology
In single-tier topology, also called collapsed-core topology, servers connect to the core switches, which provide storage services. Storage devices connect to one or more core switches, as shown in Figure 1-6. Core devices have a large number of blades to support initiator (host) and target (storage) ports. High availability is achieved using two physically separate, but identical, redundant SAN fabrics. This topology has single management per fabric and is suitable for small SAN environments.
Figure 1-6 Collapsed-Core Topology for SAN Networks
Two-Tier Topology
Two-tier topology, also called core-edge topology, is the most common SAN network topology. In this topology, servers connect to the edge switches, whereas storage devices connect to one or more core switches, as shown in Figure 1-7. Core switches provide storage services to one or more edge switches, thus servicing more servers in the fabric. Inter-Switch Links (ISLs) have to be designed in such a way that enough links/bandwidth are available between the switches to avoid congestion when servers communicate with storage devices. High availability is achieved using two physically separate, but identical, redundant SAN fabrics. This topology guarantees a single switch hop (edge to core) reachability from servers to storage. The key drawback of this topology is that core connections and the storage are in contention for extension. This topology provides room for minimal growth.
Figure 1-7 Core-Edge Topology for SAN Networks
Three-Tier Topology
In three-tier topology, also called edge-core-edge topology, servers connect to the edge switches. Storage devices connect to one or more edge switches, as shown in Figure 1-8. Core switches provide storage services to one or more edge switches, thus servicing more servers and storage in the fabric. ISLs have to be designed in such a way that enough links/bandwidth are available between the switches to avoid congestion when servers communicate with storage devices. High availability is achieved using two physically separate, but identical, redundant SAN fabrics. In this topology, a core switch is used exclusively for edge switch interconnections, allowing easy SAN expansion by storage size (adding more edge switches connected to storage) or by computing power (adding more edge switches connected to servers) independently.
Figure 1-8 Edge-Core-Edge Topology for SAN Networks
Data Center Computing Infrastructure
Computing infrastructure consists of servers that provide the processing, memory, local storage, and network connectivity that drive applications. We will discuss Cisco Unified Computing System (UCS) along with Converged Infrastructure and Hyperconverged Infrastructure products under the data center computing infrastructure. Computing infrastructure corresponds to the Unified Computing pillar of the Cisco Unified Data Center platform.
