How to Build Solid, Reliable Networks

While almost every part of a modern datacenter can be considered mission-critical, the network is the absolute foundation of all communications. That's why it must be designed and built right the first time. After all, the best servers and storage in the world can't do anything without a solid network.

Ideally, the core is composed of two modular switch­ing platforms that carry data from the edge over gigabit fiber, located in the same room as the server and storage infrastructure. Two gigabit fiber links to a closet of, say, 100 switch ports is sufficient for most business purposes. In the event that it's not, you're likely better off bonding multiple 1Gbit links rather than upgrading to 10G for those closets. As 10G drops in price, this will change, but for now, it's far cheaper to bond several 1Gbit ports than to add 10G capability to both the core and the edge.

The likely event that VoIP will be deployed

In the likely event that VoIP will be deployed, it may be beneficial to implement small modular switches at the edge as well, allowing PoE (Power over Ethernet) modules to be installed in the same switch as the non-PoE ports. Alternatively, deploying trunked PoE ports to each user is also a possibility. This allows a single port to be used for VoIP and desktop access tasks.

Either way, it's cleaner to deploy server aggregation switches in each rack and run only a few fiber links back to the core than try to shoehorn everything into a few huge switches. In addition, using server aggregation switches will allow redundant connections to redundant cores, which will eliminate the possibility of losing server communications in the event of a core switch failure. If you can afford it and your layout permits it, use server aggregation switches.

The rest of the network

Fibre Channel networks are unrelated to the rest of the network. They exist all on their own, linked only to the main network via management links that do not carry any transactional traffic. iSCSI networks can be built using the same Ethernet switches that handle nor­mal network traffic -- although iSCSI networks should be confined into their own VLAN at the least, and possibly built on a specific set of Ethernet switches that separate this traffic for performance reasons.

Either way, your storage network should mirror the main network and be as redundant as possible: redun­dant switches and redundant links from the servers (whether FC HBAs, standard Ethernet ports, or iSCSI accelerators). Servers do not appreciate having their stor­age suddenly disappear, so redundancy here is at least as important as it is for the network at large.

Normal server

Networking virtualization hosts isn't like networking a normal server, however. While a server might have a front-end and a back-end link, a virtualization host might have six or more Ethernet interfaces. One reason is performance: A virtualization host pushes more traffic than a normal server due to the simple fact that as many as dozens of virtual machines are running on a single host. The other reason is redundancy: With so many VMs on one physical machine, you don't want one failed NIC to take a whole bunch of virtual servers offline at once.

However, if you require significant back-end server-to-server communication, such as front-end Web servers and back-end database servers, it's advisable to dedicate that traffic to a specific set of bonded links. They will likely not need to be trunked, but bonding those links will again provide load-balancing and redundancy on a host-by-host basis.

While a dedicated management interface isn't truly a requirement, it can certainly make managing virtualization hosts far simpler, especially when modifying network parameters. Modifying links that also carry the management traffic can easily result in a loss of communication to the virtualization host.

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