EVOLUTION OF NETWORKED STORAGE Sonika Jindal 1, Richa Jindal 2, Rajni 3 1 Lecturer, Deptt of CSE, Shaheed Bhagat Singh College of Engg & Technology, Ferozepur. sonika_manoj@yahoo.com 2 Lecturer, Deptt of IT, Punjab Engineering College, Chandigarh. hrricha@gmail.com 3 Sr. Lecturer, ECE Deptt, Shaheed Bhagat Singh College of Engg & Technology, Ferozepur. rajni_c123@yahoo.co.in ABSTRACT Mass storage consists of more and more disk drives, collected and connected together to provide the space necessary for the large files and databases. EARLIER embedded storage was accomplished by using SCSI disk drives in the server. As storage requirements outgrew this arrangement, so manufacturers shifted to directly attached storage. Adding more servers, to fulfill the increasing demand of high storage, requires that the backup equipment must be duplicated and resource management and maintenance become more complex. This leads to the shift from direct attached storage to networked storage. The evolution of storage of data has been driven partly by the changing ways in which we use technology, and in part by the exponential increase in the volume of data we need to store. Keywords: Direct attached storage, Network Attached Storage, Storage Area Network, SCSI, Fibre Channel. 1. INTRODUCTION Information Technology requirements change every day, but one requirement that hasn t changed since the inception of data processing is the demand for fast, reliable, and massive data storage. Economic trends in the 1990s such as the rapid development of e-commerce, the globalization of business, and the mergers of already-giant corporations have only escalated the demand. Traditional data storage methods cannot keep pace with the demands placed on them. Enterprises require more information, delivered faster, and with complete reliability and traditional methods are failing to deliver. Network storage is simply about storing data using a method by which it can be made available to clients on the network. Over the years, the storage of data has evolved through various phases. This evolution has been driven partly by the changing ways in which we use technology, and in part by the exponential increase in the volume of data we need to store. It has also been driven by new technologies, which allow us to store and manage data in a more effective manner. In the days of mainframes, data was stored physically separate from the actual processing unit, but was still only accessible through the processing units. As PC based servers became more commonplace, storage devices went 'inside the box' or in external boxes that were connected directly 122 to the system. Each of these approaches was valid in its time, but as our need to store increasing volumes of data and our need to make it more accessible grew, other alternatives were needed. Although the need for storage is evident, it is not always clear which solution is right for your organization. There are a variety of options available, the most common being direct-attached storage, network-attached storage and storage area networks. It is important to focus on the specific needs and long-term business goals of your organization [1]. These three technologies for achieving higher and faster storage are described in this paper. 2. DIRECT ATTACHED STORAGE Direct attached storage remains the most common method of storing data for computer systems. Direct attached storage is used to describe a storage device that is directly attached to a host system. In Direct-attached storage, or DAS, the storage devices are part of the host computer, or directly connected to a single server, as with RAID arrays or tape libraries. Network workstations must therefore access the server in order to connect to the storage device. The traditional DAS provides a connection for a particular storage device but this strategy limits the overall network bandwidth. The simplest example of DAS is the internal hard drive of a server computer, though storage devices housed in an external box are also regarded as DAS. Direct-attached storage is a simple to deploy and have a lower initial cost when compared to networked storage. DAS is ideal for localized file sharing in environments with a single server or a few servers - for example, small businesses or departments and workgroups that do not need to share information over long distances or across an enterprise.
centralized, as well as the security, management, and backup of the data. NAS solutions are configured as file serving appliances accessed by workstations and servers through a network protocol such as TCP/IP and applications such as Network File System (NFS) or Common Internet File System (CIFS) for file access. NAS can be implemented using File Servers, host systems running NAS software (CIFS or NFS) or thin servers called appliances. Fig 1 Direct Attached Storage Model with Dedicated Storage Resources for Each Server DAS also offers ease of management and administration as it can be managed using the network operating system of the attached server. But management complexity can increase quickly if new servers are added, since storage for each server must be administered separately. Direct-attached storage is a legacy storage architecture when networking was not common and data sets were much smaller than today. A DAS environment creates islands of storage. There is no way to manage the separate storage islands as a whole. There is also a limit to how much capacity can be directly attached to each server, i.e., there are a limited number of SCSI ports. When a server goes down or is taken offline for expansion or maintenance, all data attached to it becomes unavailable. The disbursed architecture of DAS leads to high manpower costs and no central monitoring. DAS cannot provide the 24 x 7 availability that is the need of today. 3. NETWORK ATTACHED STORAGE Network Attached Storage (NAS), takes the storage devices away from the server and connects them directly to the network. It is a data storage mechanism that uses special devices connected directly to the network media. These devices are assigned an IP address and can then be accessed by clients via a server that acts as a gateway to the data or in some cases allows the device to be accessed directly by the clients without an intermediary. With NAS structure, in an environment with many servers running different operating systems, storage of data can be Fig 2 Network Attached Storage NAS servers enhance network performance by eliminating server I/O bottlenecks. In contrast to block I/O used by DAS and SANs, NAS uses File I/O. In file I/O there is no awareness of disk volume or disk sectors. Inside the NAS product an operating system or operating system kernel tracks where the files are located on disk and issues block I/O request to the disks to fulfill the file I/O read or write requests it receives. NAS is an ideal choice for organizations looking for a simple and cost-effective way to achieve fast data access for multiple clients at the file level. Some of the big advantages of NAS include the expandability; need more storage space, add another NAS device and expand the available storage. NAS also bring an extra level of fault tolerance to the network. In a DAS environment, a server going down means that the data that that server holds is no longer available. With NAS, the data is still available on the network and accessible by clients. Fault tolerant measures such as RAID can be used to make sure that the NAS device does not become a point of failure. NAS does work well for organizations 123
needing to deliver file data to multiple clients over a network. Because most NAS requests are for smaller amounts of data, data can be transferred over long distances efficiently. Designed for ease of deployment, NAS servers can be plugged directly into the network without disruption of services and management is minimal and simplified. NAS servers are an ideal means by which to consolidate file servers and backup equipment and to expand storage capacity. NAS relieves the server of storage and file serving responsibilities, and provides a lot more flexibility in data access by virtue of being independent. NAS storage scalability is limited by the size of the selfcontained NAS appliance enclosure. Adding another appliance is relatively easy, but sharing the combined contents is not. Because of these constraints, data backups in NAS environments typically are not centralized, and therefore are limited to direct attached devices (such as dedicated tape drives or libraries) or a network-based strategy where the appliance data is backed up to facilities over a corporate or dedicated LAN. Capacity cannot be re-allocated between NAS subsystems to balance out the storage usage, leaving some subsystems under-utilized and others near or at capacity. 3. STORAGE AREA NETWORK A storage area network, or SAN, is a dedicated, high performance storage network that transfers data between servers and storage devices, separate from the local area network. It is fast, reliable, and highly scalable. SAN allows storage devices to exist on their own separate network and communicate directly with each other over very fast media. Users can access these storage devices through server systems, which are connected to both the LAN and the SAN. Fig 3 Storage Area Network The use of a traditional LAN for providing a connection for server-storage, limits overall network bandwidth. SANs address the bandwidth bottlenecks associated with LAN based server storage and the scalability limitations found with SCSI bus based implementations. SANs provide modular scalability, high-availability, increased fault tolerance and centralized storage management. These advantages have led to an increase in the popularity of SANs as they are quite simply better suited to address the data storage needs of today's data intensive network environments. Fig 4 Reduction in cost per Megabyte of User Data SANs are the best way to ensure predictable performance and 24x7 data availability and reliability. This is important for companies that conduct business on the web and require high volume transaction processing. SANs have built in a wide variety of failover and fault tolerance features to ensure maximum uptime. A Fibre Channel Technology Fibre Channel is the technology developed in 1990 that is popular as a storage and processor media.sans are usually built using Fibre Channel technology, but the concept of a SAN is independent of the underlying type of network. Fibre Channel is a scalable interface for achieving high-speed data transfer rates among heterogeneous systems and peripherals. System types include supercomputers, mainframes, workstations, and desktop PCs. Peripherals include mass storage devices such as disk arrays and possibly tape libraries. The main purpose of Fibre Channel is to have any number of existing protocols over a variety of physical media and existing cable options. Since Fibre Channel is a generic data transport mechanism, it can transmit a number of existing networking and I/O protocols like SCSI, HIPPI, IPI and network protocols like, IP, IEEE 802.2 etc. Fibre Channel SANs are deployed using FC-AL (Fibre Channel Arbitrated Loop) also called Fabric or private 124
loop. These topologies enable systems to share storage using 100 MByte/sec interfaces with distances upto 10 kms. Table 1 Comparison of Different Technology The convergence of SAN and NAS will enable the customers to deploy best-of-breed network storage solutions optimized to meet their unique challenges. NAS is being seen as prelude to SAN implementation. By uniting these two systems, files can be accessed through NAS and delivered by SAN, creating a new topology shared storage. SAN and NAS have different strengths and weaknesses in different scenarios. Many large NAS systems incorporate a SAN disk back-end and many SAN implementations include NAS head unit for user network access. Products are already emerging that are hybrid of SAN/NAS, or offer gateways that transfer data between filebased and block-based data devices and networks. The speed of SAN and interoperability offered by file handling capability of NAS is a desirable combination for many applications. Further, SAN imposes 10 km point to point fibre channel limitation which can be overcome by an IP connection. It just means sending fibre channel commands over the IP network (FC/IP). Table 2 Comparison of NAS and SAN Fibre Channel allows from 2 to over 16 million ports that can be concurrently logged in to a fabric with the 24-bit address identifier, introduces new technologies like laser light and transports of different protocols simultaneously. SANs are well suited for storage sharing and building infrastructures for server and storage consolidate. SANs address performance and capacity intensive applications. SAN and NAS are both based on different architectures and therefore suited for different sectors. SAN is more suited for transaction oriented environments such as banking, whereas NAS is more suited for applications like CAD/CAM engineering, emails and file storage. Today, SANs are increasingly implemented in conjunction with NAS. With SAN/NAS convergence, companies can consolidate block-level and file-level data on common arrays. 4. CONVERGENCE OF SAN AND NAS 5. HURDLES IN IMPLEMENTING SANS 125
Even with all the benefits of SANs, several factors have slowed their adoption, which includes higher cost of implementation, management complexity and a lack of standardization. The backbone of a SAN is management software. A large investment is required to design, develop and deploy a SAN, which has limited its market to the enterprise space. While SANs remain the domain of big business, the price tag's of SAN equipment is likely to remain at a level outside the reach of small or even medium sized businesses. A majority of the costs can be attributed to software, considering the complexity that is required to manage such a wide scope of devices. Additionally, a lack of standardization has resulted in interoperability concerns, where products from different hardware and software vendors may not work together as needed. [9] Ralph H. Thornburgh, Barry J. Schoenborn, Storage Area Networks: Designing and Implementing a Mass Storage System, Prentice Hall PTR. 6. CONCLUSIONS DAS, NAS and SAN all offer tremendous benefits, but each is best suited for a particular environment. For organizations that anticipate rapid data growth, it is important to keep in mind that DAS is limited in its scalability. From both a cost efficiency and administration perspective, networked storage models are much more suited to high scalability requirements. Like all industries, storage networking is in a constant state of change. It is easier to be tempted to choose the emerging or disruptive storage technology at the time. But the best chance for success comes with choosing a solution that is cost-correct and provides long term investment protection for your organization. Digital assets will only continue to grow in the future. So we have to make sure your storage infrastructure is conducive to cost-effective expansion and scalability. It is also important to implement technologies that are based on open industry standards, which will minimize interoperability concerns as you expand your network. REFERENCES [1] http://www.storagesearch.com/san.html [2] http://www.lefthandnetworks.com [3] www.computerworld.com [4] http://www.enterprisestorageforum.com [5] http://www.brocade.com/san/ [6] Camden Ford, (2002), Comparing SANs and NAS, Information Technology, Vol. 12, No. 1, pp 57-59. [7] David Sacks, Demystifying Storage Networking, IBM storage Systems Group, San Jose, California, 2001, pp 13. [8] Garima Khanna, (2003), What s Good for You? Information Technology, Vol. 12 No. 10, pp 41-45. 126