Spine-Leaf Network

In this two-tier Clos architecture, every lower-tier switch (leaf layer) is connected to each of the top-tier switches (spine layer) in a full-mesh topology. The leaf layer consists of access switches that connect to devices such as servers. The spine layer is the backbone of the network and is responsible for interconnecting all leaf switches. Every leaf switch connects to every spine switch in the fabric. The path is randomly chosen so that the traffic load is evenly distributed among the top-tier switches. If one of the top tier switches were to fail, it would only slightly degrade performance throughout the data center.

Figure 1-5 shows a typical two-tiered spine-leaf topology.

  

Figure 1-5 Typical Spine-and-Leaf Topology

If oversubscription of a link occurs (that is, if more traffic is generated than can be aggregated on the active link at one time), the process for expanding capacity is straightforward. An additional spine switch can be added, and uplinks can be extended to every leaf switch, resulting in the addition of interlayer bandwidth and the reduction of the oversubscription. If device port capacity becomes a concern, a new leaf switch can be added by connecting it to every spine switch and adding the network configuration to the switch. The ease of expansion optimizes the IT department’s process of scaling the network. If no oversubscription occurs between the lower-tier switches and their uplinks, a nonblocking architecture can be achieved.

With a spine-and-leaf architecture, no matter which leaf switch a server is connected to, its traffic always has to cross the same number of devices to get to another server (unless the other server is located on the same leaf). This approach keeps latency at a predictable level because a payload only has to hop to a spine switch and another leaf switch to reach its destination.

Data Center Storage Infrastructure

Data center storage infrastructure consists of a dedicated storage area network (SAN), which provides high-speed network connectivity between servers and a shared pool of storage devices. The connectivity between server and storage device can be provided using various physical media; for example, fiber-optic cable uses light waves to transmit data with a connection protocol known as Fibre Channel protocol, and Ethernet cables use a storage connection protocol such as iSCSI (Internet Small Computer Systems Interface) to move and store data.

There are various benefits of using a SAN. It allows the storage disks to be connected to servers over large distances, making it ideal for enterprise data center networks. The same physical disk can be connected to more than one server, allowing for effective disk utilization. A SAN provides high availability using multiple physical paths from server to storage. SAN supports nondisruptive scalability (that is, additional storage can be added to the storage network without affecting the device currently using the network).

There are three types of SAN topologies: single-tier, two-tier, and three-tier topology.