Storage services over wide area networks

Service providers can offer low-cost connectivity of enterprise Ethernet and Fibre Channel storage networks over WANs.


The ever-increasing volume of information and the speed at which it needs to be accessed have created burgeoning demand for optical networking of storage traffic over WANs. However, this demand is not well-served by today's technologies. Access technology lacks the bandwidth and protocol support for today's enterprise data centers. Furthermore, service providers are finding it difficult, if not impossible, to build a sustainable storage service business under the existing economic model.

Highly variable data rates, tightly constrained response times, security considerations, and the demand for 24x7 availability all present challenges for storage applications. Different protocols and the high cost of bandwidth are also deterrents to networking storage over the WAN. There is a pressing need for a new optical services platform-and a new business model-to link optical enterprises to optical WANs.

Optical networking

Optical networking is becoming the technology of choice in enterprise data centers. Fibre Channel, first deployed to solve the distance limitations of SCSI, has evolved to support comprehensive switched optical networks within corporate data centers. Increases in data storage capacity and advances in switching capabilities have resulted in rapid growth of optical networking for storage area networks (SANs).

Figure 1: Optical service providers (OSPs) leverage fiber leased from fiber infrastructure providers (FIPs) to create infrastructure for storage and network connectivity services. Service providers (xSPs) deliver specialized services as outsourced storage to enterprise customers.
Click here to enlarge image

The increase in demand for network-attached storage (NAS) is one of several forces driving the growth of Gigabit Ethernet. At the same time, optical technology has been deployed to vastly increase data capacity and speed across WANs, driving down costs. However, the optical technology to efficiently service different enterprise protocols over WANs has been slow in coming. Current solutions rely on legacy copper-based networks that lack the proper capacity and protocol recognition.

To accommodate current networking applications and plan for future requirements, many enterprises are turning to outsourcing strategies in which third parties obtain, troubleshoot, maintain, and scale functions in the data center. In fact, Gartner Group forecasts that 65% of enterprises will outsource by 2004.

Build out bandwidth

To meet the expected demand of the online world, fiber continues to be installed in metropolitan area networks (MANs) and across the nation at unprecedented rates. According to Kessler Marketing Intelligence Corp., a research and consulting firm in Newport, RI, 182 million miles of fiber will be installed by the end of 2004. Today's metropolitan dense wavelength-division multiplexing (DWDM) systems offer 32 protected channels at 2.5Gb per channel, which translates to approximately 800MB of raw bandwidth, consuming only one pair of fiber strands. Future metropolitan systems will support 128 channels at 10Gbps per channel for a bandwidth of 128GB over these same fibers. SONET technology is experiencing similar leaps, advancing from OC-48 (2.5Gbps) to OC-192 (10Gbps) as the typical metro bandwidth.

To unleash this bandwidth for commercial viability, an optical services platform is required to significantly improve asset utilization, increase efficiency, and facilitate provisioning and management.

In short, the raw bandwidth is currently available for service providers to offer storage-networking services over a deterministic path and to add significant value.

The outsourcing trend has spawned a new category of specialized service providers (xSPs), focusing on areas such as storage (SSP), hosting (HSP), Internet access (ISP), and applications (ASP). Many of these xSPs outsource their network connectivity requirements to another type of provider-the optical service provider (OSP)-which specializes in optical connectivity networks. Some OSPs lease physical fiber plant from fiber infrastructure providers (FIPs), reducing time-to-market and enabling a focus on network integration, operations, and service delivery.

The unbundled optical loop

The emergence of these service providers is resulting in the "unbundling of the optical loop," which is creating new competition, lower costs, and the delivery of new high-speed services such as storage. Key mechanisms that enable an effective unbundled optical loop include

  • An optical services platform that effectively leverages existing optical infrastructure and collects clients' service performance and network data; and
  • A management system that enables service providers to exchange in real-time correlated client service and network information.

Each segment of this new service provider model can focus on its core business, which will lower costs, enable the creation of new value-added services, and ultimately enable optical networking services to a larger enterprise market (see Figure 1). With access to an abundance of bandwidth, service providers will go beyond connectivity to offer protocol-specific, value-added services to satisfy storage application requirements-all while meeting profitability goals.

Meeting the service needs of both the enterprise customer and the specialized service provider is essential for storage services to become widely available and involves additional functionality beyond simple connectivity.

There must be clear points of demarcation in the network to establish ownership and service domains between parties. These points of demarcation add the capabilities to recognize enterprise data-center protocols and add value over the WAN and are key to moving from connectivity to services. Also required are the following:

  • The ability to measure latency, allocate bandwidth, prioritize traffic, aggregate traffic, and take proactive maintenance action; and
  • Tangible cost-saving and revenue-generating benefits such as faster provisioning cycles, shorter problem-resolution times, and higher asset utilization.

The bandwidth abundance is built on very-high-speed, low-latency optical connectivity and is the foundation of the WAN. The high capacity and low latency of DWDM and SONET systems provide the ability to optimize fiber. While these technologies have been used for backhauling aggregated network traffic for some time, their widespread deployment as access devices for storage traffic to WANs has been limited due to the shortage of enterprise service features. Adding an optical services platform to the front end of a DWDM or SONET network completes these networks.

Storage services requirements

In order for a SAN to effectively span the WAN, I/O response time must be held to a few milliseconds or less. Blocks of data and commands must arrive in order and on time. Security must be provided with minimal impact on overall response time and throughput. Availability must be 99.999% to ensure business continuance. Throughput must be maintained while traffic is aggregated to maximize bandwidth utilization. In short, storage services for networking SANs across the WAN pose the most demands of any networking application.

Furthermore, enterprise data-center managers want to subscribe to services that seamlessly support their Fibre Channel and Gigabit Ethernet applications across the WAN. They want simple but comprehensive service level agreements that reflect application requirements.

Figure 2: Optical services platforms facilitate the creation of storage services from the high-bandwidth connectivity deployed in the WAN.
Click here to enlarge image

To meet these demands, an optical network designed for storage services requires a deterministic path. Traffic must travel the same path, with the same response time and with no loss of data, to be considered a viable storage service option. "Best effort" services can result in retransmission at the network level (TCP) or storage level (SCSI) and will inhibit smooth operation.

For SSPs to evolve to the next level and support centralization of storage capacity in metro areas, response time must constantly be held to a few milliseconds-even through peak-demand periods. The lack of low-cost, optically based, deterministic networking services has hindered SSPs from delivering full storage services. One temporary solution is to collocate, but this introduces inefficiencies as capacity requirements grow. With a deterministic optical storage networking service, SSPs can now migrate to a more profitable business model where massive pools of storage can be managed and allocated on demand.

OSP requirements

For an optical services platform to address these technical issues and be widely accepted, it needs to be integrated with the OSP's existing infrastructure and support value-added features. Most of this infrastructure is SONET and DWDM, which transport the bulk of data traffic and will continue to do so in next-generation networks.

As new high-capacity networks are built out, service providers will look for a platform that

  • Creates a service offering at the point of contact with the enterprise customer;
  • Establishes a point of demarcation between backbone technologies and enterprise traffic;
  • Provides efficiency and management simplicity;
  • Packs wavelengths or SONET channels to maximize asset utilization; and
  • Offers the ability to provision bandwidth, isolate faults, and deliver value-added features.

These capabilities are "must haves" for service providers to aggressively move into this market and make long-distance storage an economically viable business.

Optical services platform

In the unbundled optical loop, infrastructure providers are installing dark fiber, and OSPs are lighting it up with DWDM or SONET. And, optical networking within the enterprise has become the norm with the use of Fibre Channel for SANs, and Gigabit Ethernet for NAS and LAN (and, eventually, SAN) traffic.

Through multiplexing across an optical services platform, these two optical worlds can be linked with high-capacity, low-latency network services. The protocol-aware capabilities of the platform generate an optical service demarcation point that clearly identifies the storage network from the connectivity network. An integrated network management system, which collects/correlates the statistics from across the network to provide a single unified, end-to-end view of the optical storage service, adds another beneficial layer. This across-the-board visibility facilitates service management, increases quality of service, and reduces overall operating expenses (see Figure 2).

An optical services platform developed to deliver a ubiquitous optical networking service must integrate with the OSP's transport of choice. This means a SONET interface is required for easy access to the burgeoning installed base of optical network capacity. Multiplexing data-center traffic in a SONET payload at the point of demarcation and then transporting this over a wavelength or a SONET network achieves several objectives. The deterministic nature of these transports provides the guaranteed response time and security that storage applications require. Packets are not discarded, so traffic is not re-driven and there is no thrashing of the network.

Through the emergence of the unbundled optical loop, optical networking ser vices can be offered economically on a massive scale. Storage services across the metro area or between cities can be offered at reasonable rates, with predictable response times and widespread availability.

Optimizing bandwidth

SONET and DWDM connectivity provides security, traffic isolation, and guaranteed quality of service. These attributes are required by high-availability storage services such as real-time remote data replication, real-time restore, backup, disaster recovery, and remote disk mirroring.

Fibre Channel maintains its pipelining capabilities and collision-free operation through a complex buffer credit scheme. This scheme must be considered-and in some cases enhanced-by the optical services platform in order to optimize bandwidth over the long haul and to satisfy the most demanding storage applications. To deliver these value-added features, the optical services platform needs to be protocol-aware.

Co-existing with current technology

A critical feature of the optical services platform is support for multiple transport protocols. In today's data center, Fibre Channel is the dominant transport for SAN traffic, while Ethernet is the dominant transport for NAS traffic. The optical services platform must support both of these technologies for storage traffic as well as general networking traffic.

As storage evolves to embrace iSCSI, Gigabit Ethernet will be the transport of choice. This process has begun with the introduction of iSCSI host bus adapters (HBAs) and hybrid FC/GbE switches. Both are based on Gigabit Ethernet as the transport.

The optical services platform needs to work seamlessly with existing and new Gigabit Ethernet applications, delivering seamless access between the enterprise data center and the WAN. Demand for Gigabit Ethernet-based services over WANs (services such as Internet access, intranet access, and NAS) is already significant. Adding iSCSI to the mix will solidify the position of Gigabit Ethernet. The optical services platform must interoperate with both data-center protocols across the WAN protocols, making it simple for service providers to deliver storage services to enterprise customers.

With the appropriate technologies in place, the unbundled optical loop will greatly improve the ability of the communications network to deliver high-value, high-bandwidth optical networking services to meet the demands of today's and tomorrow's enterprise applications across the WAN. Through this improved service-delivery model, storage networking ser vices for SANs will become widely available to a vast number of enterprises, resulting in greater efficiencies and robustness for enterprise networking.

Ed Ogonek is the CEO, and Joe Scala is the director of business development at Akara (www.akara.com) in Waltham, MA.

This article was originally published on August 01, 2001