Building multi-speed SANs with scalable HBA architecture

Computer Technology Review,  August, 2003  by Phil Brotherton

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After much industry debate on 4Gb versus 10Gb speeds for next generation fabrics, the recent FCIA vote has officially cleared the way for 4Gb in the SAN. Moving forward, 4Gb is now on the standard industry roadmap for implementation in external fabrics with the full support of the FCIA. JNI and QLogic were quick to lead the customer-centric approach to the market by supporting the 4Gb standard, while other HBA companies originally suggested they would jump beyond most customers' needs to 10Gb.

For interswitch links, 10Gb has clear cost and performance advantages. However, for HBAs a focus on 10Gb is limited because it does not address two key real-world customer issues: matching bandwidth to application needs and containing IT costs. The debate over 4Gb or 10Gb as the next server to storage speed target has been largely argued as an "either/or" case based on the assumption that every application has similar bandwidth requirements and is of equal value to an organization. However, this type of argument ignores the market reality that SAN users commonly operate with mixed-speed environments and will continue to do so in the future. Widely varying customer requirements will likely present a need for higher bandwidth with the maximum performance offered with 10Gb Fibre Channel (FC), while less performance-intensive applications will be adequately served by 4Gb products with the accompanying cost savings.

The need for higher speed Fibre Channel is being driven largely by the same data-intensive applications that are the primary beneficiaries of SAN technology today, such as large-scale database and data mining applications, as well as high-definition digital video production and distribution. Ever-larger enterprise data sets will also require increased bandwidth for business continuity and disaster recovery solutions, including data replication and remote mirroring.

To offer the best technology to meet both current and future market needs, it is important to look at how companies are deploying SANs today. A reader survey by a leading storage magazine showed virtually equal distribution among users currently operating with 1Gb, 2Gb and mixed 1- and 2Gb FC environments. When asked about future purchase plans, the leading choice was narrowly 2Gb, followed closely by 10Gb and 4Gb. In other words, there's no dominant message coming from users that gives the advantage to 4Gb or 10Gb technology.

A scalable 1-2-4-10Gb FC controller, like JNI's X8, offers OEMs a common driver environment from 110Gb. Rather than being forced to over-invest in HBA capacity, end users should have the option to decide on 1, 2, 4Gb or 10Gb HBA speeds and costs based on their business requirements. HBA companies without a 110GB scalable architecture had hoped to limit next-generation HBAs to 10Gb and bypass 4Gb as a convenient way to save on research and development expenditures and avoid being late to market with 4Gb controllers and HBAs. These companies are losing sight of what is important--understanding the realities of current IT environments and creating a customer-driven design.

HBA customers have three key requirements when making buying decisions on which Fibre Channel fabric speed to support:

* Performance improvements and cost reductions for their installed 2Gb SANs

* Flexibility to seamlessly move to a 4Gb fabric, should that market emerge

* Support for 10Gb SAN fabrics for performance-critical applications

Scalable HBA Model Delivers on all Requirements

When it comes to IT budgets, a scalable HBA architecture is critical to investment protection, as the industry transitions to faster FC fabrics. Adopting the scalable HBA design also offers customers a seamless upgrade path to 4Gb by automatically negotiating between l, 2, and 4Gb speeds. Therefore, as 4Gb storage systems and switches begin to emerge, it is an attractive alternative to customers not yet using half of their 2Gb bandwidth. The upgrade to 4Gb enables customers to affordably migrate to the next performance standard without replacing already installed 1Gb and 2Gb Fibre Channel equipment. As mentioned previously, mixed-speed environments are the norm for enterprise SANs. Customers would revolt if forced to replace their entire existing SAN infrastructure simply to achieve the performance benefits of 4Gb fabrics that are only required by a small percentage of current applications.

The scalable HBA architecture not only encompasses investment protection with full backward compatibility with the installed base of 1Gb and 2Gb equipment, it offers forward compatibility by providing a common platform for 4Gb and then 10Gb products by incorporating a 10Gb Fibre Channel Attachment Unit interface (XAUI). A truly scalable HBA platform needs to offer a future-proof design that supports not just higher-speed FC performance but higher throughput server connectivity as well. At a minimum, a scalable platform must be compliant with the PCI-X 2.0 (266/533MHz) bus with an upgrade path to support the PCI Express (8X) bus.