CONTENTS 1. Introduction 2. How To Store Data 3. How To Access Data 4. Manage Data Storage 5. Benefits Of SAN 6. Conclusion
1. Introduction: A Storage Area Network (SAN) is a dedicated network that carries data between computer systems and storage devices, which can include tape and disk resources. 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. Note that the definition specifically does not identify the term SAN with Fibre Channel technology.when the term SAN is used in connection with Fibre Channel technology, use of a qualified phrase such as "Fibre Channel SAN" is encouraged. According to this definition, an Ethernetbased network, whose primary purpose is to provide access to storage elements, would be considered a SAN, such as iscsi, FCIP, or ifcp solutions. We will look at these technologies in a later module. A shorter definition might be a storage system consisting of storage elements, storage devices, computer systems, and/or appliances, plus all control software, communicating over a network. Thus, a SAN is a dedicated network for storage. It has the benefits of Channel Technology (channel technologies provide fixed connections between host systems and their peripheral devices) and Network architecture. This results in a more robust, flexible, and sophisticated approach to connecting hosts to storage resources. SANs overcome the limitations of Direct-Attached Storage, while using the same logical interface SCSI - to access storage. As business demand for data grew, DAS and NAS implementations allowed companies to store and access data effectively, but often inefficiently. Storage was isolated to the specific devices, making it difficult to manage and share. The effort to regain control over the dispersed assets caused the emergence of storage area networks (SANs). SANs had the advantage of centralization, resulting in improved efficiencies. The first implementation of SAN was a simple grouping of hosts and associated storage in a single network, often using a hub as the connectivity device. This configuration is called Fibre Channel Arbitrated Loop (FCAL). It could also be referred to as a SAN Island due to the fact that: there is limited connectivity there is still a degree of isolation As demand increased and technology improved, Fibre channel switches replaced hubs. Switches greatly increased connectivity and performance allowing for interconnected SANs and ultimately enterprise level data accessibility of SAN
applications and accessibility. This evolution architecture show the changes rapidly in store procedure. Evolution in Storage Architecture: 2. How To Store Data: SANs combine the basic functionality of storage devices and networks, consisting of hardware and software, to obtain a highly reliable, high-performance, networked data system. Services similar to those in any LAN (e.g. name resolution, address assignment etc.) allow data to traverse connections and be provided to end-users. When looking at an overall IT infrastructure, the SAN and LAN are mutually exclusive but serve similar purposes. The LAN allows clients, such as desktop workstations, to request data from servers. This could be considered the front-end network. This is where the average user would connect typically across an Ethernet network. The SAN, or back-end network also connects to servers, but in this case, the servers are acting as clients. They are requesting data from their servers the storage arrays. These connections are accomplished via a Fibre Channel network. (Note: FibRE refers to the protocol versus fiber which refers to a media!) By combining the two networks together, with the servers as the common thread, the end-user is supplied with any data they may need.
What is Fibre Channel? SAN Transport Protocol Integrated set of standards (ANSI) Encapsulates SCSI A High Speed Serial Interface Allows SCSI commands to be transferred over a storage network. Standard allows for multiple protocols over a single interface. Fibre channel is a set of standards which define protocols for performing high speed serial data transfer. The standards define a layered model similar to the OSI model found in traditional networking technology. Fibre Channel provides a standard data transport frame into which multiple protocol types can be encapsulated. The addressing scheme used in Fibre Channel switched fabrics will support over 16 million devices in a single fabric. Fibre Channel has become widely used to provide a serial transport medium over which computer systems communicate with devices such as disk storage arrays. These devices have traditionally been attached to systems over more traditional channel technologies such as SCSI. SCSI over Fibre Channel
implementations now allow these devices to be connected in dynamic Fibre Channel topologies which span much greater distances and provide a greater level of flexibility and manageability than found with SCSI. Fibre Channel networks are often referred to a networks that perform channel operations. 3. How To Access Data: Fibre channel is a set of standards which define protocols for performing high speed serial data transfer. The standards define a layered model similar to the OSI model found in traditional networking technology. Fibre Channel provides a standard data transport frame into which multiple protocol types can be encapsulated. The addressing scheme used in Fibre Channel switched fabrics will support over 16 million devices in a single fabric. Fibre Channel has become widely used to provide a
serial transport medium over which computer systems communicate with devices such as disk storage arrays. These devices have traditionally been attached to systems over more traditional channel technologies such as SCSI. SCSI over Fibre Channel implementations now allow these devices to be connected in dynamic Fibre Channel topologies which span much greater distances and provide a greater level of flexibility Storage Area Networks Both direct attached storage and storage area networks use the SCSI protocol to move data in blocks, rather than files1. In fact, from the vantage point of most operating systems, DAS and SAN storage are indistinguishable, despite the differences in their network topologies (see Figures 1 and 2). So what do storage area networks offer that traditional direct attached storage does not? SANs are designed to enable centralization of storage resources, while at the same time overcoming the distance and connectivity limitations posed by directly attached storage. Parallel SCSI interconnects limit direct attached storage devices to a distance of 25 meters, and can connect a maximum of only 16 devices. Fibre Channel SANs extend the distance limitation to 10 kilometers or more, and enable an essentially unlimited number of devices to attach to the network. These factors allow SANs to effectively uncouple storage from the server and to pool on a network where it can be shared and easily provisioned, without the problems of scaling associated with DAS. Fibre Channel interconnects delivers high performance block I/O to storage devices. The most widely adopted SAN interconnect technology, Fibre Channel, is based on serial SCSI technologies and overcomes the parallel SCSI limitations to enable essentially unlimited device connectivity over long distances. And, unlike parallel SCSI devices which must arbitrate (or contend) for the bus, FC channel devices, using switch technology, can transmit information between multiple servers and multiple storage devices at the same time However, the capital investment and the expertise required to install Fibre Channel networks components (Host Bus Adapters (HBAs), cabling and switches) can be substantial. (HBAs, like network adapter cards, install in the server and function to transmit block data.) And redundant configurations, while ensuring continuously available data, add considerably more cost and complexity.
Separating storage onto a dedicated network whether Fibre Channel or iscsi offers greater disk management efficiencies, more effective system and resource management, improved network performance, higher availability of stored resources, and more cost-effective data protection than direct attached storage can offer. Effective fabric management is the framework upon which effective SAN solutions are built. All the networked storage resources the hosts, interconnects, and storage subsystems must come together as a complete system to deliver a high performance storage solution. The software controlling SAN functionality (of both the fabric and storage array) will reside on the server, the switch and/or the storage array. Such software must: Be able to detect when storage resources are added or removed from the storage network, even in multivendor storage configurations Ensure that servers effectively share storage resources on a SAN, without interfering with ownership of storage resources, even in multiplatform environments Enable the detection and management of SAN components (such as links to the storage array), ensure they are functional, and if not, be able to fail over to an alternate component with no loss of data Help to ensure that SANs are secure Maximize throughput using high performance interconnects to and from the storage array Help realize solutions that support high availability and disaster recovery goals Enable administrators to configure storage resources on the SAN in a way that realizes the benefits of a centralized and consolidated storage model There are two approaches to obtaining an integrated SAN solution. One is to purchase a single vendor end-to-end solution. Such solutions have been available for Fibre Channel SANs for several years2. Single vendor solutions have the advantage of being complete; the disadvantages are a lack of flexibility in adding to the solution and potentially high costs. Alternatively, many organizations are installing multivendor Fibre Channel SAN solutions, which together can deliver all the same SAN benefits for lower cost. While
these solutions can create significant interoperability challenges, the challenges are diminishing as standards for ensuring interoperability emerge. In contrast, one of the significant advantages of iscsi SANs is that interoperability issues are much less problematic. 4. Manage Data Storage: The simplest SAN configuration, whether Fibre Channel or iscsi, is to deploy a minimum of two production servers attaching to a storage array. In a Fibre Channel SAN, shown in Figure 3, each server contains an HBA which connects by means of a Fibre Channel switch to a disk controller on the storage array. HBAs, although they reside on the server, are also part of the storage network. They serve first to provide the interface between the server and the attached Fibre Channel network, and second to provide I/O processing, offloading most of the server processing required for transferring data. The resulting performance is very high and very scaleable. LAN Server Server Backup Server HBA HBA Tape Library Switch Controller Storage Array MANAGE DATA STORAGE BLOCK DIAGRAM The Fibre Channel switch is an intelligent device that collects information about the SAN network topology and attached devices. Switches
Enable simultaneous communication between multiple endpoints (such as a server and storage disk) Provide capabilities for managing those connections between devices so that access is controlled (through zoning) Provide physical connectivity for failover and load balancing Although the simple configuration shown in Figure 3 provides basic connectivity to shared storage, it does not provide any protection from single point of failure problems, such as loss of a switch, controller or interconnect cable. For continual access to storage from each server, redundant components must be added: dual HBAs, switches and disk controllers. Once dual components are added in, effective fabric management becomes critical to SAN functioning. Note that an iscsi SAN has the same basic setup as that shown in Figure 3, except that a Gigabit Ethernet adapter replaces the HBA, and the connection to the disk controller on the iscsi storage target is through an Ethernet switch. 5. Benefit Of SAN: Benefits of a SAN are following High bandwidth Fibre Channel SCSI extension Block I/O Resource Consolidation Centralized storage and management Scalability Up to 16 million devices Secure Access
Some of the benefits of implementing a SAN are discussed here. A SAN uses the Fibre channel transport which is a set of standards which define protocols for performing high speed serial data transfer, up to 400 Megabytes per second. It provides a standard data transport medium over which computer systems communicate with devices such as disk storage arrays. SCSI over Fibre Channel implementations allow these devices to be connected in dynamic Fibre Channel topologies which span much greater distances and provide a greater level of flexibility And manageability while retaining the basic functionality of SCSI. Fibre Channel networks are often referred to as networks that perform channel operations. As it is a networked infrastructure, many devices and host can be attached seamlessly, upwards of 16 million devices in a SAN. This allows better utilization of corporate assets and ease of management both for configuration and security. Centralized Storage Management: Consolidating storage resources onto the network allows for a centralized approach to storage management. The central benefit of SANs, provisioning storage resources from a single pool, eliminates the problem of some server having excess storage while others have no more free disk space. For application servers like Exchange where the message stores tend to increase dramatically over time, this flexibility in scaling is an enormous advantage. Data Protection: In addition to the archival protection that tape backups provide, data can be protected against disk failure through redundancy, by using techniques such as mirroring and striping. While RAID (redundant array of independent disks) technologies can readily be deployed in direct attached configurations, the method is only useful when devices are not located more than a few meters away from the server. In contrast, RAID arrays on a SAN can be separated by several kilometers, facilitating disaster recovery scenarios that are not possible with direct attached storage. Sharing Data on the SAN: SAN contain point-in-time copies of data, known as shadow copies or snapshots. The Volume Shadow Copy Service provides the infrastructure to make point-in-time copies of single or multiple disk volumes. These shadow copies can be offloaded from the production server to a backup server where they can be backed up to tape. Such offloaded backups help keep production server performance high.
Data Consistency and Application Performance: As a method of protecting frequently used data, there are two drawbacks to the backup process. One is that, for backups to be complete and fully restorable, the file or database should not be in use. Attempting to back up data while applications are open can result in data inconsistencies. As an alternative, open files are often not backed up, or full backups are restricted to once a week at a time when applications are not in use. Such backups, however, quickly become out of date. Multipathing for High Availability: While centralizing storage on the SAN enables flexible storage provisioning and more effective resource management, it also carries an inherent risk: all of the storage is in one place. If access to the storage is lost, the entire organization loses access. Accordingly, SANs should be deployed with redundant components to prevent single points of failure, as well as with the switching mechanisms to redirect I/O requests from a nonfunctioning to a working redundant component. High Performance: SANs are designed for high performance high volume data transfers. Fiber Channel interconnects enable transfers faster than with direct attached storage. The Windows SCSI port driver, originally developed for parallel SCSI interconnects, was not designed to support the high speed performance capabilities of Fiber Channel networks. 6. Conclusion: In recent year the demand of the Storage system grows rapidly, furthermore most enterprises request the SAN System with high capacity and efficiency more reliable and secure in order to get ride of risks of data lost and services interruption. It is helpful for explosion of internet and E-commerce a tremendous amount of data has been created and made available to users.
7. References and Bibliography: IBM.com in Storage Area Network EMC-provision Storage Network www.google.com www.edufive.com www.encyclopedia.com www.allsan.com