Using DWDM for storage networking in MANs

Dense wavelength-division multiplexing (DWDM) solves the problems associated with applications such as disaster recovery in MANs.


Explosive growth in e-commerce, data warehousing, and supply chain management applications has resulted in an exponential growth in data storage requirements. These applications have become critical to business success, with employees and customers demanding uninterrupted access to corporate systems and data. Regulatory mandates in the banking, financial, and insurance industries are also driving the need for high levels of system and data backup with stringent disaster-recovery requirements.

Concurrently, the rising cost of storage management and administration has resulted in significant interest in moving from a direct-attached storage model to a more scalable and manageable networked storage model. Storage area network (SAN) technology has emerged to provide real-time transaction and database access, including data mirroring, backup, and restoration. In addition, network-attached storage (NAS) technology provides fast, simple, and reliable access to information in an IP networking environment. As a result, storage networking has become a strategic component of the IT infrastructure, addressing the need to

  • Scale, share, and maximize utilization of storage and information resources;
  • Streamline administration of the storage environment;
  • Minimize the TCO for storage; and
  • Improve data availability and integrity.

In metropolitan areas, fiber optics-a very secure, high-capacity transport medium-is becoming a readily available way to interconnect high-performance storage networks. Of the many technologies that can take advantage of fiber-optics availability, DWDM has emerged as a popular transport technology to deliver storage networking traffic safely and reliably across metropolitan area networks (MANs).

DWDM offers ultra-high capacity/perfor mance and protocol-independence, which enables companies to extend their storage networks beyond isolated islands in the data center to campus, metropolitan, and even wide-area environments. Figure 1 shows a metropolitan and campus storage networking application interconnecting both Fibre Channel SAN and IP NAS traffic.

Figure 1: An optical MAN can connect Fibre Channel SAN and IP NAS traffic.
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DWDM allows a fiber pair to be segmented into optical wavelengths, with each wavelength representing a unique connection. Applications, protocols, or organizations can be assigned a wavelength. This makes it possible to cost-effectively and transparently multiplex numerous data streams, each of which can be a different protocol and run at a different speed, across a single fiber pair. In addition, service providers can provision wavelengths to customers and charge on the basis of the number of wavelengths.

Business continuance and disaster recovery

In today's competitive business environment, system outages can be devastating. Brokerage firms and other financial institutions can lose millions of dollars per hour when systems are down, and retail sales organizations can lose hundreds of thousands of dollars per hour when customers cannot place orders. To minimize the impact of planned and unplanned outages, many enterprises are implementing system and storage redundancy with disaster-recovery capabilities.

Backup and restore is a critical component of a company's business continuance strategy. The benefits of backup and restore include

  • Data archiving for data protection against loss or corruption or to meet regulations; and
  • Remote replication of data for distribution of content, application testing, disaster protection, and data-center migration.

Critical e-business applications also require a robust disaster-recovery infrastructure. Real-time disaster-recovery solutions allow companies to safeguard their data operations by ensuring uninterrupted mission-critical services to employees, customers, and partners and guaranteeing mission-critical data is securely and remotely mirrored to avoid data loss in the event of a disaster.

Figure 2: For disaster recovery, an optical MAN can link ESCON-connected hosts and storage systems at 200Mbps.
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To ensure DWDM can support these demanding applications, optical networking vendors are working closely with storage industry leaders to deliver best-of-breed solutions and support that enable storage consolidation, business continuance, and storage outsourcing.

Data backup/recovery:
IBM, EMC environments

DWDM extends remote synchronous mirroring solutions offered by leading storage system vendors such as IBM and EMC over MANs and WANs. Figure 2 shows an IBM ESCON application for providing connectivity between host processors, storage, and peripherals at 200Mbps.

IBM's solution to system redundancy and disaster recovery is the Geo graphically Dispersed Parallel Sysplex (GDPS) technology, which supports both IBM's Peer-to-Peer Remote Copy (PPRC) synchronous and the Extended Remote Copy (XRC) asynchronous forms of remote copy. PPRC is a hardware approach that synchronously mirrors data residing on a set of disk volumes, called the primary volumes in the application site, to secondary disk volumes on a second system at another site-the recovery site. With PPRC, a copy of the data located at a remote site is synchronized with the data at the primary site. If one site is lost in a disaster, data at the other site is available to rapidly recover critical business applications. PPRC is implemented in control unit hardware, making it transparent to all host software.

XRC provides a copy of S/390 data at a remote location to be used in case the primary storage system fails. In the event of a failure, the secondary remote copy can be resynchronized quickly-without requiring duplication of all data from the primary location-for full disaster recovery.

Figure 3: Storage service providers can connect their main data center with multiple clients over an optical MAN.
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EMC's business continuance solution is the Symmetrix Remote Data Facility (SRDF) software for remote backup and recovery. SRDF provides real-time data replication between processing environments and allows a secondary volume to be geographically remote from the primary data center. SRDF can provide synchronous and asynchronous mode of operation. DWDM and Fibre Channel solutions usually operate in synchronous mode to provide remote mirroring. SRDF can also operate in an IP environment with Gigabit Ethernet or other facilities capable of transporting IP traffic.

DWDM is an excellent interconnect solution for both of these environments. DWDM provides very efficient bandwidth utilization and supports multiplexing and transport of multiple ESCON, FICON, Fibre Channel, and Gigabit Ethernet connections over a single fiber pair. Automatic protection switching can be used to provide recovery in the event of a network or equipment failure, further ensuring access to mission-critical data.

Storage network managed services

Storage networking creates broader flexibility and choice for organizations seeking to outsource storage functions to a service provider that can provide managed services such as data protection, storage-on-demand, professional services, and ser vice-level agreements (SLAs) for per- formance and availability.

Recently, storage service providers (SSPs) have emerged to provide outsourced storage solutions. SSPs address the explosive growth of storage and the current shortage of skilled storage exper tise and deliver flexible, cost-effective storage networking solutions to customers located either within their data center or geographically dispersed over an optical network infrastructure.

Most SSPs provide storage connectivity in major metropolitan areas for backup and disaster recovery; some even provide complete outsourcing services. Typically, they use a leased metro optical infrastructure provided by a managed service provider, or they have their own fiber infrastructure. The goal of many SSPs is to develop advanced services such as storage-on-demand, so that customers can simply add storage as required from the SSPs' storage pool.

Often, SSPs also build a second storage pool at another data center for backing up the primary pool, as shown in Figure 3. This secondary site is normally situated on the same metro optical ring, allowing advanced functionality such as no-data-loss remote mirroring. To succeed, a robust, high-bandwidth optical infrastructure must be in place.

The most common applications for this service-backup, mirroring, and disaster recovery-are bandwidth-intensive and latency-sensitive and therefore, well-suited for DWDM networks.

Ethernet and NAS aggregation over DWDM

For next-generation optical MAN connectivity, the combination of Gigabit Ethernet and now 10 Gigabit Ethernet over DWDM provides the required capacity and performance for key storage applications, including business continuity (backup and remote mirroring), disaster recovery, clustering, and storage outsourcing. This is largely possible because the availability of ample bandwidth and protocol independence of DWDM allow for services such as Gigabit Ethernet and Fibre Channel traffic to flow at full throughput.

DWDM systems can provide end-to-end Ethernet services across MANs or WANs that can be also used for applications such as aggregating NAS traffic. Applications, systems, or organizations can be assigned their own channels or wavelengths, which allows bandwidth to be allocated and prioritized across wavelengths to ensure quality of service for critical applications such as backup and recovery.

This end-to-end Ethernet connectivity allows service providers and enterprises to offer at least an order of magnitude higher bandwidth without requiring any change to existing enterprise network technology. In addition to high bandwidth and low cost, emerging Ethernet-based solutions can provide rapid service provisioning, priority services, and integrated management capabilities enabled by end-to-end Ethernet.


The trends are clear. Data is the most important asset for most corporations today, corporations are generating more and more data each year, and the rising cost of storing and managing all this data is leading to more storage being networked. As a result, corporations are seeking fast, reliable, and safe ways to interconnect their storage to maximize resource sharing and utilization. In the metropolitan area networking realm, DWDM has emerged as a key optical networking technology for storage networking. Delivering high-performance networking capabilities over an ultra-high bandwidth, connectionless optical infrastructure, DWDM meets today's storage networking needs with room to spare for emerging requirements.

Carl Engineer is the senior director of marketing at Cisco's Metropolitan Services Business Unit (www.cisco.com) in San Jose, CA.


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This article was originally published on December 01, 2001