Storage over SONET/SDH connectivity - Internet

Computer Technology Review, May, 2003 by Al Lounsbury

Increasingly, more and more information is becoming digital and needs to be reliably and securely stored. This information includes X-rays, MRIs, ultrasounds, video, financial data, and the list goes on. This new reality has vaulted storage systems into being an independent "core system" within IT architectures today, with very specific requirements that need to be addressed.

One such requirement is the realization that we are living in an era of increasing threats, both man-made and natural, that place all this information at serious risk of being lost. As digital content represents the life blood of companies, and given the potentially disastrous results that would occur should this data ever be lost or compromised for any reason, Disaster Recovery and Business Continuance have become critical. To mitigate the risk of losing data, enterprises are increasingly adopting storage extension technologies to replicate their business critical data to a secondary remote site. Transmitting this information over distance requires a carrier grade environment with zero data loss, scalable throughput, low latency, low jitter, high security and ability to travel long distances.

This article will discuss the business drivers and challenges for extended Storage Area Network architectures, the advantages of implementing a storage extension strategy over a SONET/SDH architecture and the critical limitations in IP storage architectures.

The Enterprise Storage Challenge

Storage systems have rarely been viewed as a "core system" within the enterprise. As a direct result, many companies have neglected to implement a Disaster Recovery (DR) plan as illustrated by various studies on this topic which show that approximately only one in four companies even have a disaster recovery plan and, of those that do, many have never tested their DR plan.

This reality has CEOs/CEOs and insurance companies now asking the question, "How fast can we recover from an unforeseen event?" The word "recovery" has gained a new level of respect and is correspondingly receiving new scrutiny within the enterprise.

These realities have enterprise companies reviewing their storage strategy for the following reasons:

* Compliance to new regulatory requirements (HIPAA, SEC),

* Improve business continuity with one common plan and infrastructure that includes remote mirroring, backup, disaster recovery and other aspects,

* Reduce operation costs by consolidating and managing a single storage infrastructure in lieu of multiple islands with multiple staff, and

* Enhance productivity with information sharing and improved SLAS.

To address these realities, there are four basic architectures for storage extension that are all available today. These include:

* Legacy access solutions that provide a low-cost solution for connecting storage systems with low bandwidth requirements.

* Storage over WDM (lambda) provides the highest bandwidth, scalability and reliability for the most demanding storage applications. This solution is dependent on the availability of fiber and greater in

cost to deploy.

* Storage over IP, which is becoming more common with the advent of the Internet and prevalence of IP. These are low reliability solutions due to the unpredictability of IP traffic and ill-suited for mission critical storage traffic.

* Storage over SONET/SDH is rapidly becoming a popular choice for subgig data rate storage requirements. Storage over SONET/SDH provides carrier grade reliability, predictability and flexibility across multiple carriers and over extended distances. This approach leverages the incumbent SONET/SDH infrastructure installed today enabling economical reliable storage services to Enterprise customers.

Table 1 illustrates the storage extension trade-offs that need to be considered before selecting an architecture regarding which storage connectivity solution to implement.

Today's Storage Area Networks

Many larger enterprise companies have already implemented storage extension utilizing WDM technology as shown in Figure 1.

In this configuration, the various enterprise sites have their Fibre Channel storage networks provisioned directly over a wavelength. This ensures that storage applications maintain their inherent bandwidth and avoid any bandwidth restrictions due to metro link speeds that are below the native Fibre Channel data rate of 1 (FC100) or 2 (FC200) gigabits per second. This configuration is common for large enterprise organizations that have intensive and business critical storage applications that need interconnecting. These requirements also justify the higher costs associated with deploying a dedicated wavelength storage connectivity service.

In order to address the needs of lower storage bandwidth needs of smaller or remote regional offices, a different, extended storage architecture is required. This architecture is storage extension via SONET/SDH, which becomes a more cost-effective infrastructure to address these sub-gigabit rate storage requirements.

Flow Control Mechanisms