Storage Basics: Storage Hubs and Switches Page 3
Hubs vs. Switches
Having reviewed Fibre Channel hubs, let's take a look at how hubs stack up against switches.
Network size - While it's really becoming less of a concern, the network size can impact the decision to go with hubs or switches. Some administrators suggest that switches should be used on networks of all sizes; in reality, if a network is comprised of fewer than 50 nodes, then hubs should do the trick. If, however, some applications are heavily used, such as full motion video streaming, then switching hubs may be needed.
Once the number of nodes grows in the network, hubs may not be able to manage the workload. Though there are no strict guidelines, in practical application, once a network surpasses 100 nodes, switches are the name of the game. A combination of both switches and hubs is sometimes used together in the network to accommodate increasing nodes.
Bandwidth - The issue of bandwidth has sent more that a few Fibre Channel hubs to the storage closet. A Fibre Channel hub, with the exception of a switched hub, is a shared device. This means that all devices attached to the hub are forced to share the bandwidth of the hub. In this case, it is possible for two or three high-performance devices connected to the hub to flood all of the ports. Fibre Channel hubs are similar to Ethernet hubs in that all ports see traffic from all other ports. This approach often leads to bandwidth congestion and sometimes security concerns. A switch, however, has completely independent ports, and each port can simultaneously support the maximum bandwidth limits of the topology used.
Because of the bandwidth limitations of the traditional hub, hubs are not the best choice on storage networks where heavy audio and video data is regularly exchanged.
Security - In the IT world today, security is a hot topic. Security may also come into play when deciding between hubs and switches. Some hubs do not allow zoning on the Fibre Channel network. Zoning is much like creating virtual LANs on an Ethernet network, and it provides a way to allow only certain ports to communicate with other certain ports in the fabric. The issue is obviously not a concern where hubs allow for network zoning.
Scalability - When it comes to scalability, switches are the clear winner. Switches are very scalable and will accommodate future growth. Hubs are a different story. Because of their security concerns and the fact that they use bandwidth sharing, they are not scalable to larger networks. If a network is small but is expected to experience rapid growth, switches are again the answer.
While being somewhat inferior in terms of performance, hubs are still entrenched in many Fibre Channel networks. Knowing what types of hubs are available, what they are designed to do, and what limitations they present are all important considerations when managing a Fibre Channel network. While hubs and switches are an integral part of the Fibre Channel network, we still need a way to connect these devices. In the next Storage Basics article, we'll take a look at the Fibre cabling and connectors used to connect hubs, switches, and other devices to the network.