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QLogic and HP Simplify SAN Design
Todd Owens|Wednesday, November 21, 2012
Marketing Manager, HP

What if I told you there was a way to reduce the complexity and cost of SAN connectivity by decreasing the number of tiers, while still providing scalability and high performance bandwidth?

First let’s look at the typical legacy Fibre Channel storage area network (SAN) design which connects servers to edge switches and in turn, these switches connect to core switches (or SAN directors) to provide high performance bandwidth aggregation to shared storage. This core-edge, or two-tiered approach, is deemed necessary to provide sufficient connectivity to multiple server paths and at the same time provide necessary bandwidth for access to the shared storage pool.

The Old Way is Not Always the Best

The challenge with this legacy approach is that the more a SAN grows, the more complexity and costs are added to the mix. With the advent of Fibre Channel stacking architecture, like that found in HP SN6000 Stackable Fibre Channel switches, edge and core capabilities are integrated into a single platform framework, reducing the complexity and cost of the SAN fabric.

Traditional Core/Edge SAN Design vs SAN Design with Stackable Switches

Based on QLogic technology, HP SN6000 Stackable Fibre Channel switches support 20 device ports and four stacking ports in a 1U configuration. The four stacking ports are dedicated for inter-switch link (ISL) communications. These native 10Gb Fibre Channel ports can be upgraded to 20Gb Fibre Channel with a software license key. The dedicated ISL ports allow multiple switches to be connected together in a non-disruptive manner, and provide the high performance Fibre Channel core connectivity found in the traditional two-tier architecture.

Stacking Architecture Combines Core and Edge Functionality

The 20 device ports and dedicated stacking ports of the HP SN6000 Stackable Fibre Channel switches enable the SAN administrator to build a simplified fabric, where edge and core connectivity are integrated. This means one product provides both functions. That's one product to buy and one product to manage, which leads to more efficiency in the data center.

Anatomy of a Stacking Port

The ISL ports on HP SN6000 Stackable Fibre Channel switches are based on XAUI (10Gb Attachment Unit Interface, with the X being roman numeral for 10) connections that deliver 10Gb throughput utilizing four signal lanes per connection. Introduced by the IEEE 802.3ae 10Gb Ethernet Task Force, this technology provides an ideal mechanism for high speed connectivity between devices.

Each ISL connection has four lanes of 3.1875Gbps bi-directional bandwidth, or a total available bandwidth of 12.75Gbps per connection. This means two switches can be connected together using these four connections that provide more than 50Gbps in aggregate bandwidth. In addition, the ports can be upgraded to 2X their native speed using a software license key, enabling each port to run at 25.5Gbps, or 102Gbps total aggregate bandwidth for connecting HP SN6000 switches together.

The Economics of Stacking – Save Dollars to Invest Elsewhere

With this kind of bandwidth available through only four connections, the dedicated ISL stacking ports in the HP SN6000 Stackable Fibre Channel switches can prove to be very beneficial from a total cost of ownership (TCO) perspective. In fact, a study by Wikibon suggests that the stacking architecture can lower TCO over a four-year period by as much as 74 percent compared to conventional ISL connections that use standard device ports. The primary reason for this is that stacking switches via dedicated, high-speed ISL ports is much more efficient than using standard device ports as the SAN fabric grows. This is because the legacy approach wastes device ports exponentially as switches are added, while the stackable approach leaves all device ports free for their intended use.

Another huge benefit of a stacking architecture is that the high-speed 10Gb or 20Gb stacking ports can replace the need for directors or core switches. This greatly simplifies the overall architecture of the fabric, reducing the number of required components (switches), and since these switches can function as one stack, they can be easily managed from a single console. This means one management application, one login and full management of the fabric.

A third benefit is trunking, a technique that simplifies switch management and optimizes performance by combining multiple ISLs into one common "trunk." While some vendors require IT administrators to purchase additional software, costing between $5,000 and $7,000, to enable this feature, trunking is automatic with HP SN6000 Stackable Fibre Channel switches and no additional licenses are required. A feature called “adaptive trunking" comes standard with all HP H-series Fibre Channel switches and ensures the flow of Fibre Channel data between switches is always balanced and bottlenecks in the ISL paths are eliminated.

The bottom line is SAN administrators can build flatter, more efficient, high-performance SAN fabrics by implementing Fibre Channel switches with a stacking architecture. The overall fabric is greatly simplified both in terms of required components and fabric management. This reduces the overall cost and provides significantly better TCO. As SAN administrators look to upgrade their legacy 2Gb or 4Gb Fibre Channel SAN environments, the expression, “out with the old, and in with the new” may apply. A stackable architecture can really pay off.

For more information on QLogic, HP and HP SN6000 Stackable Fibre Channel switches, go to: and

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