In computing, a storage area network (SAN) is an architecture to attach remote computer storage devices (such as disk arrays, tape libraries and optical jukeboxes) to servers in such a way that, to the operating system, the devices appear as locally attached. Although cost and complexity is dropping, as of 2007, SANs are still uncommon outside larger enterprises.
By contrast to a SAN, network-attached storage (NAS) uses file-based protocols such as NFS or SMB/CIFS where it is clear that the storage is remote, and computers request a portion of an abstract file rather than a disk block.
Network types
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Most storage networks use the SCSI protocol for communication between servers and disk drive devices. However, they do not use SCSI low-level physical interface (e.g. cables), as its bus topology is unsuitable for networking. To form a network, a mapping layer is used to other low-level protocols:
-Fibre Channel Protocol (FCP), mapping SCSI over Fibre Channel. Currently the most common. Comes in 1 Gbit/s, 2 Gbit/s, 4 Gbit/s, 8 Gbit/s, 10 Gbit/s variants.
-iSCSI, mapping SCSI over TCP/IP.
-HyperSCSI, mapping SCSI over Ethernet.
-FICON mapping over Fibre Channel (used by mainframe computers).
-ATA over Ethernet, mapping ATA over Ethernet.
-SCSI and/or TCP/IP mapping over InfiniBand (IB).
Storage sharing
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The driving force for the SAN market is rapid growth of highly transactional data that require high speed, block-level access to the hard drives (such as data from email servers, databases, and high usage file servers). Historically, enterprises were first creating "islands" of high performance SCSI disk arrays. Each island was dedicated to a different application and visible as a number of "virtual hard drives" (or LUNs).
SAN essentially enables connecting those storage islands using a high-speed network.
However, an operating system still sees SAN as a collection of LUNs and is supposed to maintain its own file systems on them. Still, the most reliable and most widely used are the local file systems, which cannot be shared among multiple hosts. If two independent local file systems resided on a shared LUN, they would be unaware of the fact, would have no means of cache synchronization and eventually would corrupt each other. Thus, sharing data between computers through a SAN requires advanced solutions, such as SAN file systems or clustered computing.
Despite such issues, SANs help to increase storage capacity utilization, since multiple servers share the same growth reserve on disk arrays.
In contrast, NAS allows many computers to access the same file system over the network and synchronizes their accesses. Lately, the introduction of NAS heads allowed easy conversion of SAN storage to NAS.
Benefits
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Sharing storage usually simplifies storage administration and adds flexibility since cables and storage devices do not have to be physically moved to move storage from one server to another.
Other benefits include the ability to allow servers to boot from the SAN itself. This allows for a quick and easy replacement of faulty servers since the SAN can be reconfigured so that a replacement server can use the LUN of the faulty server. This process can take as little as half an hour and is a relatively new idea being pioneered in newer data centers. There are a number of emerging products designed to facilitate and speed up this process still further. For example, Brocade offers an Application Resource Manager product which automatically provisions servers to boot off a SAN, with typical-case load times measured in minutes. While this area of technology is still new, many view it as being the future of the enterprise datacenter.
SANs also tend to enable more effective disaster recovery processes. A SAN could span a distant location containing a secondary storage array. This enables storage replication either implemented by disk array controllers, by server software, or by specialized SAN devices. Since IP WANs are often least costly method of long-distance transport, the Fibre Channel over IP (FCIP) and iSCSI protocols have been developed to allow SAN extension over IP networks. The traditional physical SCSI layer could only support a few meters of distance - not nearly enough to ensure business continuance in a disaster. Demand for this SAN application has increased dramatically after the September 11th attacks in the United States, and increased regulatory requirements associated with Sarbanes-Oxley and similar legislation.
Consolidation of disk arrays economically accelerated advancement of some of their advanced features. Those include I/O caching, snapshotting, volume cloning (Business Continuance Volumes or BCVs).
SAN infrastructure
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SANs often utilize a Fibre Channel fabric topology - an infrastructure specially designed to handle storage communications. It provides faster and more reliable access than higher-level protocols used in NAS. A fabric is similar in concept to a network segment in a local area network. A typical Fibre Channel SAN fabric is made up of a number of Fibre Channel switches.
Today, all major SAN equipment vendors also offer some form of Fibre Channel routing solution, and these bring substantial scalability benefits to the SAN architecture by allowing data to cross between different fabrics without merging them. These offerings use proprietary protocol elements, and the top-level architectures being promoted are radically different. They often enable mapping Fibre Channel traffic over IP or over SONET/SDH.
Compatibility
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One of the early problems with Fibre Channel SANs was that the switches and other hardware from different manufacturers were not entirely compatible. Although the basic storage protocols FCP were always quite standard, some of the higher-level functions did not interoperate well. Similarly, many host operating systems would react badly to other operating systems sharing the same fabric. Many solutions were pushed to the market before standards were finalized and vendors innovated around the standards.
The combined efforts of the members of the Storage Networking Industry Association (SNIA) improved the situation during 2002 and 2003. Today most vendor devices, from HBAs to switches and arrays, interoperate nicely, though there are still many high-level functions that do not work between different manufacturers’ hardware.
SANs at home
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SANs are primarily used in large scale, high performance enterprise storage operations. It would be unusual to find a single disk drive connected directly to a SAN. Instead, SANs are normally networks of large disk arrays. SAN equipment is relatively expensive, therefore, Fibre Channel host bus adapters are rare in desktop computers. The iSCSI SAN technology is expected to eventually produce cheap SANs, but it is unlikely that this technology will be used outside the enterprise data center environment. Desktop clients are expected to continue using NAS protocols such as CIFS and NFS. The exception to this may be remote storage replication.
SANs in the Media and Entertainment
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Video editing workgroups require very high data rates. Outside of the enterprise market, this is one area that greatly benefits from SANs.
Per-node bandwidth usage control, sometimes referred to as quality-of-service (QoS), is especially important in video workgroups as it lets you ensure a fair and prioritized bandwidth usage across your network. Avid Unity and Tiger Technology MetaSAN are specifically designed for video networks and offer this functionality.
Storage virtualization and SANs
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Storage virtualization refers to the process of completely abstracting logical storage from physical storage. The physical storage resources are aggregated into storage pools, from which the logical storage is created. It presents to the user a logical space for data storage and transparently handles the process of mapping it to the actual physical location. This is of course naturally implemented inside each modern disk array, using vendor's proprietary solution. However, the goal is to virtualize multiple disk arrays, made by different vendors, scattered over the network, into a single monolithic storage device, which can be managed unifromly.
Sunday, September 9, 2007
Storage area network (SAN)
Surface Computing (Microsoft Surface)
Microsoft Surface is a forthcoming product from Microsoft which is developed as a software and hardware combination technology that allows a user, or multiple users, to manipulate digital content by the use of natural motions, hand gestures, or physical objects. It was announced on May 29, 2007 at D5, and is expected to be released by commercial partners in November 2007. Initial customers will be in the hospitality businesses, such as restaurants, hotels, retail, and public entertainment venues.
Overview
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Surface is essentially a Windows Vista PC tucked inside a black table base, topped with a 30-inch touchscreen in a clear acrylic frame. Five cameras that can sense nearby objects are mounted beneath the screen. Users can interact with the machine by touching or dragging their fingertips and objects such as paintbrushes across the screen, or by setting real-world items tagged with special barcode labels on top of it.
Surface has been optimized to respond to 52 touches at a time. During a demonstration with a reporter, Mark Bolger, the Surface Computing group's marketing director, "dipped" his finger in an on-screen paint palette, then dragged it across the screen to draw a smiley face. Then he used all 10 fingers at once to give the face a full head of hair.
In addition to recognizing finger movements, Microsoft Surface can also identify physical objects. Microsoft says that when a diner sets down a wine glass, for example, the table can automatically offer additional wine choices tailored to the dinner being eaten.
Prices will reportedly be $5,000 to $10,000 per unit. However Microsoft said it expects prices to drop enough to make consumer versions feasible in 3 to 5 years.
The machines, which Microsoft debuted May 30, 2007 at a technology conference in Carlsbad, California, are set to arrive in November in T-Mobile USA stores and properties owned by Starwood Hotels & Resorts Worldwide Inc. and Harrah's Entertainment Inc.
History
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The technology behind Surface is called Multi-touch. It has at least a 25-year history, beginning in 1982, with pioneering work being done at the University of Toronto (multi-touch tablets) and Bell Labs (multi-touch screens). The product idea for Surface was initially conceptualized in 2001 by Steven Bathiche of Microsoft Hardware and Andy Wilson of Microsoft Research. In October 2001, a virtual team was formed with Bathiche and Wilson as key members, to bring the idea to the next stage of development.
In 2003, the team presented the idea to the Microsoft Chairman Bill Gates, in a group review. Later, the virtual team was expanded and a prototype nicknamed T1 was produced within a month. The prototype was based on an IKEA table with a hole cut in the top and a sheet of architect vellum used as a diffuser. The team also developed some applications, including pinball, a photo browser and a video puzzle. Over the next year, Microsoft built more than 85 early prototypes for Surface. The final hardware design was completed in 2005.
A similar concept was used in the 2005 Science Fiction movie The Island, by Sean Bean's character "Merrick". As noted in the DVD commentary, the director Michael Bay stated the concept of the device came from consultation with Microsoft during the making of the movie. One of the film's technology consultant's associates from MIT later joined Microsoft to work on the Surface project.
Surface was unveiled by Microsoft CEO Steve Ballmer on May 29, 2007 at The Wall Street Journal's D: All Things Digital conference in Carlsbad, California.Surface Computing is part of Microsoft's Productivity and Extended Consumer Experiences Group, which is within the Entertainment & Devices division. The first few companies to deploy Surface will include Harrah's Entertainment, Starwood Hotels & Resorts Worldwide, T-Mobile and a distributor, International Game Technology.
Features
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Microsoft notes four main components being important in Surface's interface: direct interaction, multi-touch contact, a multi-user experience, and object recognition. The device also enables drag and drop digital media when wi-fi enabled devices are placed on its surface such as a Microsoft Zune, cellular phones, or digital cameras.
Surface features multi-touch technology that allows a user to interact with the device at more than one point of contact. For example, using all of their fingers to make a drawing instead of just one. As an extension of this, multiple users can interact with the device at once.
The technology allows non-digital objects to be used as input devices. In one example, a normal paint brush was used to create a digital painting in the software. This is made possible by the fact that, in using cameras for input, the system does not rely on restrictive properties required of conventional touchscreen or touchpad devices such as the capacitance, electrical resistance, or temperature of the tool used (see Touchscreen).
The computer's "vision" is created by a near-infrared, 850-nanometer-wavelength LED light source aimed at the surface. When an object touches the tabletop, the light is reflected to multiple infrared cameras with a net resolution of 1280 x 960, allowing it to sense, and react to items touching the tabletop.
Surface will ship with basic applications, including photos, music, virtual concierge, and games, that can be customized for the customers.
Specifications
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Surface is a 30-inch (76 cm) display in a table-like form factor, 22 inches (56 cm) high, 21 inches (106 cm) deep, and 84 inches (214 cm) wide. The Surface tabletop is acrylic, and its interior frame is powder-coated steel. The software platform runs on Windows Vista and has wired Ethernet 10/100, wireless 802.11 b/g, and Bluetooth 2.0 connectivity.
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Electronic Product Code
The Electronic Product Code, (EPC), is a family of coding schemes created as an eventual successor to the bar code. The EPC was created as a low-cost method of tracking goods using RFID technology. It is designed to meet the needs of various industries, while guaranteeing uniqueness for all EPC-compliant tags. EPC tags were designed to identify each item manufactured, as opposed to just the manufacturer and class of products, as bar codes do today. The EPC accommodates existing coding schemes and defines new schemes where necessary.
The EPC was the creation of the MIT Auto-ID Center, a consortium of over 120 global corporations and university labs. The EPC system is currently managed by EPCglobal, Inc., a subsidiary of GS1, creators of the UPC barcode.
The Electronic Product Code promises to become the standard for global RFID usage, and a core element of the proposed EPCglobal Network.
Structure
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All EPC numbers contain a header identifying the encoding scheme that has been used. This in turn dictates the length, type and structure of the EPC. EPC encoding schemes frequently contain a serial number which can be used to uniquely identify one object.
EPC Version 1.3 supports the following coding schemes:
-General Identifier (GID) GID-96
-a serialized version of the GS1 Global Trade Item Number (GTIN) SGTIN-96 SGTIN-198
-GS1 Serial Shipping Container Code (SSCC) SSCC-96
-GS1 Global Location Number (GLN), SGLN-96 SGLN-195
-GS1 Global Returnable Asset Identifier (GRAI) GRAI-96 GRAI-170
-GS1 Global Individual Asset Identifier (GIAI) GIAI-96 GIAI-202 and
-DOD Construct DoD-96
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