SAN consolidation with director-class switches


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Directors deliver more bandwidth

Bandwidth is another key advantage of director-class switches for environments that need high total I/O bandwidth. The Brocade DCX directors provide up to 256 Gbps of total bandwidth per slot (or blade) of 16, 32 or 48 ports. The DCX also has a local switching capability that can provide up to 384 Gbps of bandwidth for ports in the same port group within a 48-port blade. The Cisco 9500 series provides 96 Gbps or 192 Gbps per slot (or switching module) of 24 or 48 ports. Each vendor can provide performance data for their product that shows how well their systems do under heavy loads, but the main point is that they can handle very heavy loads of storage I/O traffic. In addition, these directors also have the capability to have several 10 Gbps Fibre Channel ports that are used for ISLs to trunk traffic between switches or directors. This ISL capability allows large SAN fabrics to be constructed in a core-edge type of topology, where one or more directors are at the core of the SAN and smaller, fixed port-count switches are deployed at the edge of the SAN. As server virtualization becomes more common and the load on physical servers becomes greater, the need for high bandwidth in the FC infrastructure also increases and directors become a more appealing alternative to regular switches.

High-availability benefits of directors

High availability is another design feature of directors. Normally, directors are

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deployed in business-critical settings where very high uptime is one of the key criteria of service-level agreements. Directors typically have redundant components so that there's no single point of failure. This covers the basics such as redundant hot-pluggable power supplies and cooling fans, and includes redundant core processing and switching components, as well as redundant World Wide Name (WWN) cards. These high-availability features allow for nondisruptive software or firmware upgrades.

Some of the redundant components operate in an active/passive mode, where one component is active and the other is in standby mode, ready to take over in the event of a failure of the active component. If there's a hardware failure on a port or port card in a director, the port card can be removed and replaced without losing use of the entire director. With an equivalent failure in a fixed port-count switch, the entire switch typically has to be taken offline for repair or replacement. Directors are designed to stay up and running so that host servers don't lose access to their storage data. Of course, all of the high-availability capabilities add to the cost of these systems.

High-end features of directors

Directors also provide a number of advanced features, some of which aren't available in smaller, fixed port-count switches. Directors from Brocade and Cisco each support the concept of virtual SANs, FICON for mainframes, and provide features for long-distance connections using FCIP, iSCSI, dense wavelength division multiplexing (DWDM), SONET and other protocols. The specific implementations differ slightly when comparing the two vendors' products, but these directors are designed to be the central hub for a complex SAN that not only handles local FC traffic, but can send the Fibre Channel traffic over distances to remote sites.

Because of their modular design, directors can adapt to new requirements. For example, specialty blades that support connecting to dark fiber, hardware encryption, 10 Gb Ethernet (10 GbE), Fibre Channel over Ethernet (FCoE) and other features are available today, and the directors' designs also support future requirements in the same infrastructure without having to replace the entire unit.

Management of directors and the SAN fabric is critical, and these directors provide solid management software that can do performance monitoring, quality of service (QoS) , bottleneck detection, advanced zoning and a myriad of other functions. The directors can also pass management data using SNMP to higher-level management software platforms.

This was first published in April 2010

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