In my latest webinar, Data Center Game Changer: Understanding the Impact of Data Center Fabrics, we discussed the latest trend of implementing switch fabrics to provide low-latency and high-bandwidth east-west communication for large virtualized data centers.

During the webinar, I highlighted a recent survey by Enterprise Strategy Group where 16% of respondents indicated that they have already begun implementing flat data center fabric with another 38% planning to do so.

As confirmed by several of the questions I received following the webinar, another 36% of the survey respondents said they wanted to learn more about switch fabrics before making the decision to implement.

One of the most frequently asked questions surrounds migrating from traditional three-tier architecture to fat-tree architecture in existing data centers.

Following are a few key considerations to help you on your migration path.

It Does Not Have to be All or Nothing


While there is a compelling business case for using fat-tree architecture in purpose-built, greenfield data center builds, especially for virtualized networks and cloud computing, they can also be deployed alongside existing traditional architectures.

fabric switch architectures

For example, legacy applications can remain on traditional three-tier architecture while newer, more demanding applications that generate more east-west traffic can be deployed on the switch fabric. This is often accomplished using separate fat-tree pods. The interconnection between the traditional and fabric switch architectures can be accomplished at higher levels within the switch hierarchy, such as core switches and routers. The ability for switch fabrics to coexist with traditional architectures can help ease the migration process. In other words, switch fabrics do not have to be all or nothing.

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Interoperability Matters


Switch vendors use different methods for implementing data center fabrics. Before any reconfiguration or upgrade is performed at any layer, ensuring interoperability between equipment is essential. Using open standard protocols is important if using switches from different vendors, especially with fabric switch architectures that introduce multiple active paths between equipment. If using switches from different vendors, it is also important to address bandwidth and traffic handling capability for peak loads.

Compatibility and interoperability of cabling is also a consideration. For example, the cabling media chosen for connecting access switches to servers must be compatible with both—if using SFP+ direct attach cables, the servers must be equipped with SFP+ ports. Interoperability of the cabling is also a consideration—some access switches may require proprietary cables for connecting to servers. Be sure to check with your switch vendors about open protocols and interoperability during the early stages of the decision-making process.

Rely on Your Vendors


When it comes to eliminating tiers in the network, there are several considerations involved—from networking platforms and operating systems, to modifying configurations and replacing hardware. It is important to determine the operational impact of each step and ensure a fallback position in the event of issues when replacing existing legacy switches. While some data centers may be better equipped to migrate to fat-tree architecture with installation of new access layer switches and port extenders, this is not typically the norm. Most data centers will need to maintain their existing three-tier architecture (or a portion thereof) until the new architecture is up and running.

The details for migrating to fat-tree are best answered by your system integrator and switch vendor, depending on your current situation and needs. Most switch vendors offer professional services and experts to help with the migration process—from planning, testing and design, to the switchover and post-upgrade troubleshooting. Vendors also offer a variety of tools and technologies that can help with migration and cut over.