Current SAN infrastructure products, however, are bound by the limits of monolithic approach bottlenecks. The disconnect between applications and infrastructure makes it difficult to introduce new, more flexible technologies such as storage virtualization and information lifecycle management. This disconnect is perpetuated by monolithic SAN products that attempt to provide additional services in a single platform. Creating more responsive, intelligent and flexible storage networks requires a new strategy for SAN design and a new architecture for SAN interconnect products. A modular approach to SAN design enables customers to preserve the integrity of their current SAN deployments while non-disruptively adding advanced storage services that more closely align with varying application requirements.
Aligning Infrastructures to Applications
Information management is an integral component of modern business operations. The sheer mass of data generated by day-to-day business transactions, however, presents an unprecedented challenge for both large and small enterprises. It is no longer sufficient to simply process a customer order and then go on to the next transaction. To be competitive, enterprises must analyze millions of transactions to determine customer preferences, buying trends, cyclical needs and market dependencies. The steady accumulation of data must not only be accommodated, but mined for maximum value. In addition, regulatory compliance is setting new standards for data preservation, security and availability. Businesses must not only manage current exchanges, but maintain historical data as transactions pass through their normal lifecycles.
The introduction of responsive technologies such as information lifecycle management and content management of both structured and unstructured data is now forcing an alignment of applications and infrastructure. The data created by business transactions is often dynamic and changes in value over time. Currently, however, the underlying infrastructure that supports data storage and transport does not provide the flexibility to respond to data's varying business value.
SANs, for example, are typically deployed to provide a single class of service in terms of data delivery and availability. A large enterprise may have monolithic storage arrays, large, highly available directors and expensive server platforms with failover software and dual path connectivity to the SAN. In such configurations, all data, regardless of current business value, is given first class service. To reduce costs and align with the business realities of varying data value, SANs must provide the flexibility to offer multiple classes of service, in terms of cost of storage, availability and security.
Native Fibre Channel SANs are layer 2 (link layer) networks that provide basic storage services such as fabric building, fabric logon, state change notification and high performance frame switching. The layer 2 nature of native Fibre Channel SANs enables very high performance within datacenter circumference and provides the foundation for higher level storage services.
Over the past several years, the storage industry has introduced new technologies to further enhance data storage and delivery. Storage over IP, for example, has enabled affordable data replication and other remote applications over enormous distances. iSCSI now provides a means to economically connect second-tier servers into an existing enterprise SAN and to build lower cost IP SANs for small businesses and departments. New SAN security products allow customers to encrypt sensitive storage data in flight or at rest on disk or tape. SAN routing now enables customers to segment their storage networks and avoid building large flat networks susceptible to fabric reconfigurations and disruptive state change broadcast storms. Diverse storage virtualization technologies are simplifying storage administration through pooling of storage assets and enable data snapshots and replication in heterogeneous environments. And new content management and lifecycle management products are helping align information handling requirements and the SAN infrastructure in order to reduce costs and improve data retrieval.
Advanced storage services sit between the higher level business applications and the conventional SAN transport layer. A variety of advanced services may be inserted between the SAN transport and the upper level applications to provide flexibility, responsiveness and more efficient and economical management of storage data.
Collectively, these advanced capabilities are taking SANs to the next level. Previously confined to the narrow circumference of the datacenter and cost-justifiable only for the most mission-critical business applications, SAN technology can now scale throughout a global enterprise while offering a wide range of advanced services. How, specifically, these advanced services are incorporated into SAN design will determine whether these new technologies are disruptive to current deployments or cost-effectively extend the power of existing SANs.
Monolithic or Modular
Although customers may see immediate business value in ILM, storage virtualization, SAN routing, distance technologies or other enhanced services, the adoption of new solutions is often accompanied by risk. The technical challenge for providing higher levels of storage services, then, is to add more layers of enhanced functionality without undermining the stability of current SAN operations. At the same time, management of new services must be integrated into existing SAN administration so that the value of new services is not lost in additional complexity of operation. Few customers are willing to risk the integrity of data for the sake of a new technical solution, and none want to implement a new solution that in the end adds complexity to their lives.
Currently, two very different SAN architectures have emerged to address the problem of incorporating advanced services within the storage network. The monolithic approach attempts to combine all advanced services as well as traditional SAN switching operations into a single, large platform, which becomes the basis of a new SAN. In effect, the monolithic architecture combines layer 2 transport and upper layer services in a single hardware platform. The modular approach, by contrast, views advanced services as discrete components that can be added or layered on to an existing layer 2 SAN. The initial selection of a monolithic or modular design has profound implications for how storage networks can adapt to changing business requirements over time.
The Big Box Rule
A monolithic SAN architecture attempts to provide higher level storage services within the confines of a single large chassis. A monolithic SAN director, for example, may provide traditional switching operations on port blades, while supporting advanced services such as distance, routing or storage virtualization on specialized blades that slot into the director chassis. At first glance, this approach is attractive in that it implies a more unified way to manage traditional and new SAN services. As new services are required, they can be simply installed as blades into an existing platform.
The monolithic, blade-and-chassis-based strategy, however, has already exposed substantial issues in terms of deployment, scalability and ongoing management. Traditionally, SAN directors have a central, critical function to provide: high performance and high availability switching of storage data frames. The 99.999% availability, redundancy and phone-home capability of leading SAN directors are essential complements to enterprise-class storage. The introduction of new hardware components in the form of services blades may potentially undermine the central role that directors have fulfilled.
A virtualization blade, for example, may be composed of PC logic, memory, a small IDE drive and an operating system to support a virtualization application. The additional power requirement and heat dissipation as well as PC-class components on a blade may place too great a burden on a director chassis already loaded with traditional port and switching cards. In terms of scalability, it may not be possible to populate the chassis with additional enhanced services blades without exceeding the power and cooling capability of the director.
Another significant issue that has emerged is microcode management. As more feature-specific blades are introduced into a common chassis, new levels of microcode must be loaded onto the director. The more services, the more complex the microcode. As additional feature blades are supported, it become increasingly difficult to proactively test against all the permutations of feature blade combinations. The traditional benefit of being able to hot swap port blades in a director, for example, becomes a significant challenge when the hot swap of distance, routing, iSCSI or virtualization blades must also be supported. Ensuring the stability of basic switching services may be at risk as more feature-specific blades are introduced.
Monolithic architectures assume a single-vendor fabric environment, with replacement of an existing SAN infrastructure with a new one. To gain the benefit of advanced storage services, the customer must commit to a particular vendor's product for basic layer 2 SAN services as well. Such a deployment entails some disruption to production since at some point boxes must be replaced and re-cabled. In addition, even within a single vendor offering, blades from one director model may not be compatible with the chassis of another model, requiring maintenance of not only different model port and switch cards, but advanced services blades as well.
From a management standpoint, bladed services appear to have an advantage in being fully integrated into a director management application. While this meets the customer's desire to simplify management of basic and advanced services, there is little benefit in "single pane of glass" management if the management application is constantly required to debug power, heat or microcode conflict issues. The real challenge is to both simplify management and reduce the need for management attention. This challenge is more readily met by stepping outside the big box approach and adopting a modular strategy.
The Modular SAN
The modular SAN architecture makes a clear distinction between the traditional layer 2 SAN functionality and the addition of advanced services. This decoupling between layer 2 infrastructure and higher level services provides flexibility in substituting components at either level without requiring a wholesale swap of the entire SAN infrastructure. Instead of combining traditional SAN transport services with new services in the same hardware platform, a modular approach implements advanced services as separate building blocks. Consequently, the addition of new services such as storage virtualization can be accomplished without disrupting ongoing SAN operations or requiring downtime for replacing director chassis and re-cabling of the production SAN.
Because a modular architecture preserves the customer's existing SAN infrastructure investment, the cost of introducing advanced services is more easily contained. As new services or expansion of acquired services are required, modular building blocks can be selectively applied as needed. Likewise, upgrading or expanding the layer 2 SAN transport does not impact the advanced services operations. The customer has the flexibility to target specific applications by, for example, the addition of a new director for higher availability for one application group or the introduction of routing or virtualization for another. In a monolithic approach, by contrast, both basic and advanced services are bound together within a single cage.
The separation of traditional layer 2 transport services and advanced storage services into different hardware modules also preserves the integrity of the five nines (99.999% availability) director, allowing the director to focus on its prime mission of high performance switching. Since advanced services are supplied via separate hardware platforms, they pose no risk to the internal operation of the director itself, impose no additional power or heat dissipation issues and do not introduce marginal PC-class components. The stability of basic storage services required for data delivery, backup and other SAN operations is thus assured.
Likewise, there is no melding of microcode between basic and advanced services support. As before, director platform microcode retains its focus on providing robust SAN delivery services. Separately, microcode for each advanced services module is focused on providing that specific enhanced functionality. This also facilitates the selective upgrading of either basic or advanced services without posing an interdependent code risk.
In terms of interoperability and backward compatibility, a modular SAN architecture enables the overlay of new storage services on existing SAN transport hardware. A customer with a mix of directors and switches in a core-edge SAN design, for example, can add enhanced services while avoiding the disruption of a forklift change of the SAN. Given that many enterprise customers have deployed very large SAN configurations over time, minimizing disruption is an essential requirement when considering the adoption of new, higher level storage solutions.
From a management standpoint, a modular architecture supports full integration of basic and advanced services administration. A virtualization services module, for example, can be represented in a management application as an integral component of director management, with no separate domain ID or management identity as a separate unit. This meets the customer requirement to streamline and simplify the administration of both basic and advanced services and places the focus appropriately on storage service functionality, not specific hardware configuration.
Conclusion
The next wave of SAN evolution is focused on higher level storage services that fully exploit the fundamental advantages that storage networks enable. Fabric-based services such as storage virtualization may be implemented in a monolithic, single chassis director architecture, or in a modular building block approach. Monolithic solutions present inherent vulnerabilities in terms of scalability, disruption and undermining the original role of SAN directors. In contrast, a modular architecture allows the introduction of advanced services on a foundation of existing SAN infrastructure, thus preserving high performance, availability and scalability. McDATA continues to lead the market with next generation storage services modules that provide richer and more powerful storage solutions while maximizing the value of our customers' SAN investment.
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