The Way to SANity

Storage Area Network (SAN) solutions are becoming a key Enterprise application and a promising addition to the service portfolio of many Telecom carriers.

 Val Golan

In the information age, data has become valuable above all: It is a resource, but also an output, an intangible asset, and a wealth to protect. Computer networking revolves around means to acquire, transmit, exchange and store data. The volume of data that companies commonly process and store today has reached numbers that could not be conceptualized a few years ago. This unprecedented growth has created a huge demand in data management, and led to the development of Storage Area Networks, or SANs. Industry analysts consider information as the lifeblood of organizations and data storage crucial to an enterprise’s viability. A Gartner Dataquest report published in Aug. 2002 predicts $21 billion in total worldwide revenue for external storage, growing to almost $23 billion by 2006. Of that total, Gartner estimates that worldwide SAN revenue will comprise $6.5 billion in 2002, growing to $13.5 billion by 2006, a compound growth rate of 17 percent.

A SAN is dedicated to data storage and clearly separated from the LAN (Local Area Network) and the WAN (Wide Area Network). It links the storage-related resources connected to one or more servers.  It is often characterized by its high interconnection data rates (Gigabits/Second) between member storage peripherals and by its highly scalable architecture.

Offloading tasks, such as backup, from LANs and WANs is vital today when network loads and bandwidth availability are criteria for measuring performance and even profits. Backup windows have shrunk dramatically and some environments have entirely eliminated them, since entire data networks and applications often require round-the- clock availability.

The combined factors of great data volume, LAN congestion and 24/7/365 operation have steered the data storage demand toward the SAN technology.  

Evolution from DAS to SAN

The first data storage model integrated a number of servers, to each a dedicated storage system would be attached. Named DAS for Direct Attached Storage, this technology has physical limitations that impede system growth and scalability. The information contained in each server-storage is difficult to share, and servers that have fully consumed their own storage cannot use excess capacity available elsewhere. IT administrators are faced with the time-consuming task of managing these distributed storage systems individually. Since system growth has to be carefully planned and over-provisioned, storage costs in the DAS environment can easily become the costliest item in an IT budget.

The emergence of Storage Networking architectures, such as NAS (Network Attached Storage) and SAN, has brought the promise of a more dynamic technological concept. Instead of attaching storage to individual servers, NAS provides file storage directly to the LAN for use by network applications and users. A SAN creates a dedicated storage network, separate from the LAN, using Fibre Channel (FC) or Internet Protocol (IP) switches that provide block storage for use by servers and workstations. 

Although NAS and SAN are both storage networks, they work with different protocols and are completely isolated from one another. A SAN typically interconnects using FC technology, while a NAS uses IP technology, most often with the Ethernet protocol. The clear advantage of SAN over NAS is its separation from the LAN: First, it can transport traffic at speeds much greater that those supported by the LAN, and more importantly, it frees the LAN from carrying backup data. This ultimately contributes to better LAN performance and allows the IT department to optimize server and network utilization. 

SAN architecture

SANs can be seen as comprised of two elements: A storage system and a network. The storage system includes disk storage, tape libraries, and SAN-management software. The network includes cabling, switches and different adapters. Host Bus Adapters are used to connect the hardware (servers and peripherals) to the network wiring or bus, while switches allow centralized connection with routing capability, in a similar way to a LAN switch.

SANs are comprised of hardware equipment, such as hubs, switches, bridges, servers and backup devices interconnected through diverse cabling media. Highly specialized SAN software addresses the needs to operate the different system components while enhancing the performance, data availability and manageability of the SAN.

SANs can be based on several types of high-speed interfaces. In fact, many SANs today use a combination of different interfaces. Currently, Fibre Channel (FC) is the de facto standard in most SAN environments. FC is an industry-standard interconnection method and high-performance serial I/O protocol that is media independent and supports simultaneous transfer of multiple protocols. Additionally, SCSI is frequently used for sub-interfaces between internal components of SAN members, such as between raw storage disks and a RAID (Redundant Array of Inexpensive Disks) controller.

ă Dot Hill Systems

Fig. 1  SAN Hardware Architecture

Benefits of SAN

Transitioning from DAS to storage networking dramatically enhances the way an enterprise can manage information. Old limitations are removed and new techniques enabled. Omar Barraza, Director of Product Management at Dot Hill Systems, a California-based Storage Systems vendor, lists the key business benefits for deploying a SAN as follows: 

·          Downtime Reduction

Using a network to separate storage and servers allows configuration changes to occur without affecting other operations. Storage networking also introduces redundancy that eliminates potential points of failure between applications and information. Storage networking reduces both planned and unplanned downtime. 

·          Unlimited Online Scalability

A storage network eliminates the physical constraints on scalability, as the storage is now independent of the servers. Information capacity or processing power can be increased when needed simply by connecting additional storage systems or application servers. Adding switches grows the size of the network to any size needed. Storage networks scale without impacting operations. 

·          Simplified Management

Consolidating DAS information onto a storage network greatly minimizes the number of storage management instances requiring administration. The resulting reduction in workload on IT staff directly decreases storage management costs. Industry analysts agree storage networking and information consolidation lower the total cost of ownership (TCO) of IT infrastructure. 

·          Improved Capacity Utilization

Moving storage onto a network enables superior control over capacity allocation. The exact amount of storage needed by an application can be assigned, and additional capacity can be added later if needed. More efficient use of available capacity improves the return on investment (ROI) of storage assets. 

·          Faster Backup and Restore

Ordinary backup and restore becomes unpredictable when protecting large amounts of information due to the volatility of LAN traffic. Using a storage network eliminates these issues and enables faster protection and recovery times. It also improves network application performance by freeing the LAN bandwidth otherwise used during backup and restore. 

·          Disaster Recovery and Protection

The switches used within storage networks accommodate very long-distance connections. The FC switches of a typical SAN can interconnect across a campus or even across town. IP Switches can be connected at intercontinental distances. Linking FC and IP switches into a common storage network is a vital component of disaster recovery and protection. 

·          Broader Information Sharing

The “any-to-any” design of a storage network enables an enterprise to easily and effectively make centrally stored information available to all users. SAN provides for the sharing of capacity among servers and workstations, while NAS enables the sharing of files among applications and users. An enterprise can “mix and match” SAN and NAS to suit its exact needs.

Additional techniques, such as “Serverless” backup and server clustering, further enhance the high availability, reliability and cost-effectiveness of SANs.

In “Serverless” backup operations, host computers (servers) do not handle the backup data, but merely direct and monitor the backup without actually moving the data. The backup data is copied directly from disk to tape, or disk to disk, by “intelligent” storage peripherals. Freed from the routine data transport burden, server resources can be put to more productive uses. The backup or tape server becomes a “backup coordinator” rather than a mere data mover. Serverless backup takes LAN-free backup a step further since it removes backup traffic from both the LAN and the backup server.

Server Clustering refers to grouping together SAN servers for the purpose of enhancing their performance and/or providing failover protection in the event that a member server malfunctions. Uninterrupted and seamless availability of data and applications during and after a server failure is a primary benefit of a server cluster architecture within a SAN.

Toward Convergence: SANs, LANs and WANs

In today’s global environment, an increasing number of IT operations have to be performed over geographically dispersed sites. Data storage frequently involves high-speed data transmission with FC over existing long-distance fiber infrastructures. Fiber optics, with its great transport capacity, exceptional safety, security and immunity properties, can be optimized into further cost-efficiency with DWDM (Dense Wavelength Division Multiplexing) systems. Allowing parallel transmission of up to 32 different channels on a fiber pair, DWDM technology is emerging in both the core and access components of the metro network. It provides telecom carriers with greater bandwidth (multiple Gigabits) with low investment costs (protocol-transparent DWDM is completely interoperable with legacy equipment). The benefits of connecting SAN networks over metro DWDM systems are clear to most players in the IT and Telecom worlds. Benny Schollin, Managing Director of TSS (Total Storage Solutions) in Sweden, comments: “In Sweden, where SANs are highly developed and the fiber optic infrastructure is far-reaching, we have integrated SAN applications among a variety of companies with remote sites. We have been using DWDM systems to optimize on the fiber media and transmit great amounts of data for storage over distant locations ”.

An example of such applications is the private telecom network built by two Northern German publishers to secure data transmission between their separate headquarters and their common IT site. The Oldenburg and Bremen publishers need to back-up every night 500 to 600 gigabits of data, and send to the printers all the daily newspaper’s articles. The two remotest sites are located at a distance of 65 km (40 miles), but the PANDATEL DWDM system would have allowed longer distances. Using a scalable system, the IT department wanted to keep the option for growth and extension open.

The most common way to extend SANs into WANs is to provide Fiber Channel extension. This allows the interconnection of different SANs in a point-to-point configuration, using transport mechanisms such as SONET or ATM.  Another commonly used storage protocol is ESCON (Enterprise System Connection) with data rates of 200 Mbps. Because of its data rate and protocol-based technology, ESCON is not easily extended over current available transport systems such as SONET/SDH rings. DWDM systems provide channel aggregation for transport regardless of the protocol or technology, so they will work with any kind of FC extension as well as point-to-point ESCON.

ă Dot Hill Systems

Fig. 2 Convergence of SAN, LAN and WAN

With the growth of packet-based technologies and the cost-effectiveness of Gigabit Ethernet, an increasing number of optical WANs are becoming IP-based at the core. Ethernet/IP LANs are easily extended into these IP WANS, but Fibre Channel, optimal for storage networks thanks to its high speed and low overhead, is not IP-based and prevents SANs from reaching into the WAN. Fibre Channel over IP (FCIP) and Small Computer System Interface (SCSI) over IP (iSCSI) are two technologies aimed at bridging the worlds of SANs and WANs. Using these evolving technologies, SANs can be extended across multiple locations in multi-point configurations.

When the SAN meets the WAN, the LAN or the MAN (Metropolitan Area Network), a whole new paradigm emerges: SAN internetworking. SAN, LAN, and WAN integration brings data networking and data storage into a homogeneous point of convergence.

SAN internetworking allows carriers to expend their portfolio of Enterprise service offerings with little or no modification of their WAN infrastructure. Mission-critical customers such as financial institutions are highly receptive to these new services in the perspective of secure transmissions and fast disaster recovery. The current trend toward cheaper and greater bandwidth, together with the growing demand for readily available, safe data storage, has made SAN a key application to offer, at minimal investment costs.

"Carriers can use DWDM in a shared infrastructure model that provides unparalleled scalability and redundancy in SAN applications at a lower total cost of ownership than dark fiber alone," said Brian McConnell, director of marketing for WDM products in Tellabs' optical networking group. "Using this, carriers can generate new revenue that can quickly add to their bottom line."

SAN clearly delivers new opportunities to carriers, and increased benefits to the Enterprise.

Val Golan is Director of Marketing and Product Management at PANDATEL, Inc.