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What is a SAN?
A storage area network (SAN) is a high-performance subnet, probably (but not necessarily) based on fibre channel, whose primary purpose is the transfer of data between computer systems and storage elements and among multiple storage elements. One can think of a SAN as an extended and shared storage bus. A SAN consists of a communication infrastructure, which provides physical connections, and a management layer, which organizes the connections, storage elements, and computer systems so that data transfer is secure and robust.

What are the Market Drivers for SANs?
The limitations in speed, distance, and connectivity of SCSI technology prompted the search for an alternative method to access storage devices. The need for LAN-free backups and data sharing started the initial move toward SAN technology. These necessities and the desire to keep all data on-line and accessible 24 hours a day to an increasingly global and/or Internet-based user population are driving current adoption.

Market Drivers:

  • Backup Capacity: Increasing data storage requirements and the need for 100% availability of applications have overwhelmed SCSI backups across the LAN.

  • Capacity Growth: IDC and Gartner Group estimate that data is growing at a rate of over 85% annually. To put this in perspective a 750GB

  • System Flexibility/Cost: SANs are storage-centric networks that provide easy scalability, allowing servers or storage to be added independently of each other.

  • Availability/Performance: The use of a storage data transmission protocol like SCSI permits the transfer of large amounts of data with limited latency and overhead.

Why are Storage Area Networks Needed?
Traditional means for connecting servers and storage can no longer satisfy today's requirements for fast access to massive amounts of data. SCSI technology uses parallel cabling which severely limits speed, distance and the number of attached storage devices. Configuring SCSI (Small Computer Systems Interface) connections to support terabytes of data is impractical. In addition, traditional server/storage connections make the server the exclusive owner of its attached storage. As computing environments move from a server centric to data centric model, access to shared data resources becomes critical. Storage Area Networks are an enabling technology that allow storage resources to be shared in order to provide continuous, faster, easier access to data.

What are the Benefits of a SAN?
The primary benefits of a SAN are:

  • Availability: A single copy of data is accessible to any and all hosts via multiple paths.

  • Reliability: Dependable data transportation ensures a low error rate, and an ability to recover from failures is provided.

  • Scalability: Servers and storage devices may be added independently of one another, and do not depend on proprietary systems.

  • Performance: Fibre Channel (the standard method for SAN interconnectivity) has a 100MB/sec bandwidth and low overhead, and it separates storage and network I/O.

  • Manageability: Emerging software and standards for both FC-AL and Fibre Channel fabric allow single centralized management and proactive error detection and correction.

  • Return On Information Management: Due to increased redundancy and superior manageability, as well as the ability to add storage and servers independently of one another SANs provide a lower cost of ownership and a Higher Return On Information Management (ROIM).

When should I use a Switch versus a Hub?

  • Hubs: Hubs are perfect for small, entry-level environments and systems. The typically cost less and offer a lower throughput the switches.

  • Switches: Data-intensive, high-bandwidth applications such as backup, video editing, and document scanning can make full use of switches. Due to their redundant data paths and superior manageability switches are also perfect when high availability is required.

Are there reasons to use Switches instead of Hubs in a SAN?
Switches provide several advantages in a SAN environment.

  • Failover Capabilities: In a switched fabric, in the event that a single switch fails, other switches in the fabric remain operational. A Hub based environment typically fails if a single hub on the loop fails.

  • Increased Manageability: Switches support the Fibre Channel Switch (FC-SW) standard, which makes addressing independent of the subsystem's location on the fabric and provides superior fault isolation and high availability. FC-SW also allows host to better identify subsystems connected to the switch.

  • Superior Performance: Switches offer "multiple-transmission data flow", in which each fabric connection can simultaneously maintain a 100MB/sec throughput. A hub offers a single data flow with an aggregate throughput of 100MB/sec.

  • Scalability: Interconnection switches provide thousands of connections without degrading bandwidth. A hub-based loop is limited to 126 devices.

  • Availability: Switches support the on-line addition of subsystems (servers or storage) without for re-initialization or shutdown. Hubs require a Loop Initialization (LIP) to reacquire subsystem addresses whenever changes occur on the loop. A LIP typically takes 0.5 seconds and can disable a tape system that is in the process of doing a backup.

How does a SAN differ from a LAN or WAN?
A SAN is similar to a LAN, in that it is a methodology of connecting systems together with standardized hardware and software protocols. A SAN differs from a LAN is two main ways.

  • Storage versus Network Protocol: A LAN uses network protocols that send smaller "chunks" of data with increased communication overhead. This reduces bandwidth. A SAN uses storage protocols (SCSI) that sends larger "chunks" of data with reduced overhead and increased bandwidth.

  • Server Captive Storage: LAN based systems connect servers to clients, with each server owning and controlling access to its own storage resources. Storage must be added to a server rather than directly to the LAN. A SAN allows storage resources to be added to the network enabling any server to directly access storage resources.

How do I manage a SAN?
There are two basic methods for SAN management.

  • SNMP (Simple Network Management Protocol): SNMP is based on TCP/IP and offers basic alert management. This allows a node to alert the management system of failures (drive, fan, power….). However SNMP does not offer proactive management and lacks security.

  • Proprietary Management Protocol: The second way to manage a SAN is to use a proprietary management protocol. There are a number of manufacturers who provide SAN management software (see SAN Management). In either case to run management software typically requires a separate terminal (such as an NT server) connected to the SAN. This enables additional capabilities, such as zoning (security), mapping, masking, as well as backup and restore and fault management.

What is a SAN Manager?
A San Manager is a proprietary Storage Area Network management software, which enables management of fibre channel attached storage in a highly efficient manner as an administrative cluster. SAN Managers enable systems to use a common pool of storage devices on a Storage Area Network. Using a SAN Manager, administrators can assign storage from pools of available capacity when and where it is needed.

Who are the major SAN vendors?
Many key industry players support the evolution of SANs and are involved in the development of the industry. These companies include ITIS Services, Hitachi Data Systems, Hewlett-Packard, Compaq, StorageTek, Brocade, Gadzoox, Veritas, Legato, Computer Associates, Oracle, DataCore, Ancor, Vixel, Sun, Dell and a number of other industry leaders. The most active of these leaders have established themselves as members of the Storage Network Industry Alliance (see SNIA).

What is the SNIA?
The SNIA (Storage Network Industry Alliance) is an international, not-for-profit organization made up of 55 voting member companies, who collaborate in an effort to bring reliable storage solutions to the broader marketplace. The SNIA is a central point of contact for the industry accelerating the development and evolution of standards.

Voting Members Include: (January 2000)



3Com Corporation
Ancor Communications
Axis Communications
BMC Software
Brocade Communications Systems
Chaparral Technologies
CommVault Systems
Compaq Computer Corporation
Computer Network Technology
Crossroads Systems
DataCore Software
DataDirect Networks
Data General
Dell Computer
EMC Corporation
Emulex Corporation
Eurologic Systems
Exabyte Corporation
Fujitsu Computer Products
HighGround Systems

Hitachi Data Systems
INRANGE Technologies Corporation
Intel Corporation
ITIS Services LLC
Legato Systems
LSI Logic
McDATA Corporation
Mercury Computer Systems
Meridian Data, Inc.
MTI Technology Corp.
Network Appliance
Novell, Inc.
Online Technologies Group
Overland Data Inc.
Pathlight Technology, Inc.
Seagate Technology
Sterling Software
Storage Area Networks Ltd.
Sun Microsystems
Tivoli Systems
Tricord Systems
Troika Networks
Veritas Software

What is Fibre Channel?
Fibre Channel is a standards-based, gigabit transport that is optimized for storage and other high-speed applications. Currently implemented in 1 gigabit (200MBps full duplex) speed, Fibre Channel will support up to 400MBps full duplex transfer speeds in the near future. There are three topologies based on Fibre Channel - point to point, arbitrated loop and fabric. Arbitrated loop and fabric provide the underlying infrastructure of most SAN implementations today. Fibre Channel supports high speed transport, long distances (up to 60 km), and up to 16 million devices in extended network configurations. By introducing the scalability and flexibility of networking to the server/storage relationship, Fibre Channel is enabling new storage applications for clustering, disaster recovery, and shared resource requirements.

Who is Guiding the Development of Fibre Channel Standards?
Fibre Channel standards have been developed through ANSI (American National Standards Institute) committees. Vendors and end-users are also represented by industry bodies such as the Fibre Channel Industry Alliance (FCIA) and the Storage Networking Industry Alliance (SNIA). Cooperative efforts by vendors and customers are driving both standardization and interoperability to streamline the adoption of SANs. ITIS Services is a voting member of the SNIA and an active participant in today's industry standards.

What is Fibre Channel "Fabric"?
In the early days of Fibre Channel, the concept of a universal "Fabric" was popular as a means of supporting Fibre Channel's topology independence. Its value has since been enhanced with the advent of point to point and FC-AL topologies. The Fibre Channel Fabric was designed as a generic interface between each node and the physical layer interconnect of these nodes. By adhering to this interface, any Fibre Channel node could communicate over the "Fabric" without being required to have specific knowledge of the interconnecting scheme between nodes. A "Fabric" is similar to a telephone switch in which we make a call and the party at the other end answers, all without having detailed knowledge of the interconnection method between the two points.

What is Fibre Channel Arbitrated Loop?
Arbitrated loop is a shared architecture, which supports 100MBps or 200MBps full duplex speed. Analogous to token ring, multiple servers or storage devices can attach to the same loop segment. Up to 126 devices may be attached to a FC-AL, although the majority of arbitrated loops are deployed with from 4 to 30 devices. Since the loop is a shared transport, devices must arbitrate for access to the loop before sending data. Fibre Channel provides a superset of commands to provide orderly access and ensure data integrity.

What is a GBIC?
A GBIC is a gigabit interface converter. A removable transceiver commonly used in Fibre Channel switches, hubs and host bus adapters. A transceiver converts one form of signal into another or from fibre optic signals to electrical signals. A critical component of high speed data transfer, GBIC's ensure the quality of signaling and data integrity.

What is an Interconnect?
Capable of speeds 100 times faster than current networks, Interconnect is the pipeline used for high-speed, high-bandwidth data access within a storage area network. It connects all of the pieces of a SAN and provides scalability, connectivity, performance and availability.

What is The Difference Between SAN and NAS?
Storage Area Networks (SAN) and Network-attached Storage (NAS) are similar, in that they both represent a convergence of storage and networking technologies. However, they are also entirely different. NAS products, such as Network Appliance Filers and Auspex servers are storage devices fronted by a thin server client that is directly attached to the messaging or public network. These products tend to be optimized for file serving purposes only. Storage Area Networks are separate networks dedicated to storage devices and traffic. SANs provide greater flexibility and additional functionality over a NAS. However each of these approaches has their merits, it is generally agreed that SANs represent the future of storage connectivity. NAS devices will continue to perform their specific functions but shall migrate, over time, to the Storage Area Network model.

How Quick will the SAN Market Develop?
Industry projections vary, and some are quite optimistic. According to Dataquest, an industry watchdog, the SAN marketplace will grow 89% compounded annually between 1999 and 2003. According to IDC SANs are expected to grow ten-fold by 2002. To put a dollar figure on this, according to IDC the overall disk storage market for the year 2000 will exceed $80 billion dollars.

How do SCSI Tape Drives Connect to A Fibre SAN?
Fibre Channel to SCSI bridging products enable connection of SCSI tape drives/libraries, or SCSI disk subsystems, to Fibre Channel-based SANs.

Evolution of SAN's
With any emerging technology, prospective end users need to be informed about how, what and when standards will be adopted and approved by industry manufacturers and developers. Armed with this knowledge, IT decision makers may begin to assess where SAN's can be safely deployed throughout the enterprise without risking loss of infrastructure investment. The SAN industry is represented by several hardware, software and service consortiums. These include: SNIA (Storage Network Industry Alliance), FCIA (Fiber Channel Industry Association) and the FCA (Fiber Channel Alliance). In an effort to promote and adopt universal SAN standards, these groups co-develop hardware and software protocols. Many vendors within the industry are working towards an "open" solution to enable end users the flexibility to mix and match products and achieve a true "best of breed" data storage processing environment. Several switch manufacturers, for example, are working to ensure that their products can co-exist within a SAN. This is a key objective since proprietary solutions may effectively forfeit the greatest possible return on information management (ROIM) and lock users out from readily exploring alternatives. The SAN industry has universally adopted fiber channel arbitrated loop (FC-AL) as a protocol for exchanging data within switched and non-switched environments. Switched fabric, on the other hand, has not emerged with a complete set of standards agreed on by the industry. While there are successful installations of switched fabric SAN's, users are generally advised to implement FC-AL until standards have been set for switched protocol. Switch manufacturers are releasing products that communicate FC-AL and are fabric upgradeable. Despite the delay in producing a fully supportable set of switched fabric standards, end users can still benefit substantially from the performance gains within SAN architectures using FC-AL.

The potential of SAN technology is staggering. For starters, fiber optic technology offers an unprecedented leap in bandwidth capacity. Existing SAN backbones support 1.025 GB throughput; 2GB will be available sometime in 2000 and additional exponential leaps will occur in increasingly shorter timeframes. As bandwidth becomes a commodity, data exchange will be unfettered and storage will be measured in multiple petabytes (1 Petabyte=1000 Terrabytes). To meet the demand for fiber interfaces, storage vendors are designing their platforms with fiber backplanes, controllers and disk modules. Future offerings include "serverless" backup technology. This feature will remove the traditional server interface from backup libraries and enable faster backups. Presently, heterogeneous platforms may only share the physical storage space within a SAN. As standards emerge, Unix, NT and other open systems will enable data sharing through a common file system.

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