Design & Solutions for the Storage Area Network

Best Practices

Thursday, 23 October 2008 18:48

Written by Jennifer Cline

When specifically addressing the needs of the high-density storage area network (SAN) environment, the aforementioned factors are especially important; additionally, due to the specific needs of the storage area network and its components, additional factors must be considered. The cabling infrastructure in this environment must provide for system manageability, flexibility and scalability to meet both current and future needs.

These needs cannot be met when a single choice or decision is made with a focus solely on the physical topology or solutions for the cabling infrastructure. Both of these areas (topology and cabling technology) must be evaluated in tandem to provide the optimal benefit. Without optimal choices in both of these matters, compromises to the needs of the data center may be required. As a result, concerns such as increased time of deployment, increased complexity of infrastructure management and cooling issues may be encountered.

As the SAN environment grows, the need for high-port-count switching also grows. This need is met with devices such as SAN directors, which provide port counts ranging from 128 to 528 ports (or 1056 optical fibers) in a single device. Cabling such high-density devices is not trivial. One of the fundamental challenges for SANs is the large volume of optical fiber cabling that must be managed in cabinets that store large modular (core) switches. With installations consisting of point-to-point jumpers, or patch cords, between the director and connected devices such as server or storage, “day 1” installations as well as continued operations and maintenance with moves, adds and changes can become challenging, if not impossible.

 
 
LC/LC Duplex Patch Cord
When individual jumper cables are used to make each port connection, densities of several hundred cables concentrate along the sides of the cabinets, blocking airflow and making it difficult to administer moves, adds and changes.

The first step in achieving success in cabling of the SAN is to employ an optical cabling infrastructure design based on TIA-942 recommended guidelines. To do this, a main distribution area (MDA) is identified to provide a central patching area for connectivity to all areas of the data center. Many of the electronics contained within the data center are then located in what TIA-942 refers to as equipment distribution areas (EDAs). These areas commonly contain racks or cabinets with servers, or “server farms,” storage devices and SAN switches or directors. Optical cabling is then installed from the central patching area in the MDA to all areas requiring connectivity in a star topology.

 
Optical cabling infrastructure design based on TIA-942 recommended guidelines

In addition to establishing the topology of the cabling infrastructure, product solutions to be utilized should be evaluated. To meet the specific needs of high-density SAN directors in this environment, an MTP® harness assembly using high-density cabling and connectivity is recommended.

 
MTP harness assembly

To enhance these features, the harness assemblies are engineered and tailored to fit specifically with devices manufactured by leading SAN director suppliers. The pre-engineered MTP harness assembly technology consists of a 12-fiber cable terminated with an MTP connector on one end and furcated to 6 LC Duplex connectors at the other end. The length(s) of the overall assembly as well as the LC Duplex-terminated legs are designed to provide optimal routing into the SAN director while minimizing slack and congestion across the director ports, as well as in the cabinet or rack vertical management space. The MTP termination provides connectivity into the backbone cabling infrastructure via an MTP interconnect at a local patching field in the SAN director cabinet. This patching field can be located in a traditional rack-mount housing within the cabinet or rack, or within the cabinet vertical management space. Mounting of the patching field in the vertical manager eliminates the use of valuable rack space and provides a clean, un-cluttered environment for the SAN director.

 
Optical connectivity for SAN Director using zero rack space

To enhance the physical technology of the pre-engineered MTP harness assembly, utilization of a port-mapping architecture provides completed documentation for the installation, prior to installing a single cable or connector. With diagrams that outline the connectivity from each port on the SAN director to each port at the local patching field to each port at the MDA, the installer can follow this step-by-step guidance for an installation requiring minimal time. Additionally, this documentation provides a means for administering moves, adds, and changes, by eliminating the need to trace links, or channels, within the infrastructure. The connectivity from the SAN director ports is easily identified at the MDA with the port-mapping diagrams, allowing for simple identification of connectivity.

Utilizing a high-density infrastructure in combination with the tailored, MTP harness solution, as described, provides the following key benefits:
• With a move from typical patch cord installations to high-density, MTP-terminated cabling infrastructures, a reduction in bulk cabling volume exceeding 50 percent is realized in data center pathways
• Continuing the use of high-density, MTP-terminated technologies with harness assemblies eliminates over 75 percent of the bulk cabling volume within the cabinet vertical manager(s)
• With multifiber harness connectivity enabled by the MTP connector, cabling infrastructure installation time is reduced by over 75 percent when compared to traditional cabling methods
• Pre-engineered harnesses eliminate issues with slack management, as well as the time traditionally required to “plan/design” custom assemblies for SAN director connectivity
• Complete with port-mapping diagrams, the harness assemblies are installed in a “connect-the-dot” method, speeding the installation process
• With a technology that is designed to work with SAN director deployments, the cabling solution aligns with each line card, minimizing disruption to line cards with live traffic when upgrades or changes are required at the SAN director

With a combination of structured cabling installations and a high-density, optical cabling solution, the data center SAN cabling infrastructure is no longer a cause for concern. The infrastructure now alleviates issues with design, installation, and management, meeting the need for flexible, scalable connectivity.

About the Author: Jennifer Cline, Market Manager, Corning Cable Systems

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