Branch: Information Technology Seminar title:INTERNET SCSI
ABSTRACT
In a world where networks are common place and data storage requirements increase at such a dramatic rate, it is inevitable that both network and storage technologies converge. The iSCSI (Internet Small Computer Systems Interface) protocol unites storage with networking enabling block level data transfer over an IP based network infrastructure. The iSCSI protocol is based on two widely used and proven protocols: SCSI commands and protocols for storage and the IP protocol for networking
iSCSI is an Internet Protocol (IP)-based storage networking standard for linking data storage facilities, developed by the Internet Engineering Task Force (IETF). By carrying SCSI commands over IP networks, iSCSI is used to facilitate data transfers over intranets and to manage storage over long distances. The iSCSI protocol is among the key technologies expected to help bring about rapid development of the storage area network (SAN) market, by increasing the capabilities and performance of storage data transmission. Because of the ubiquity of IP networks, iSCSI can be used to transmit data over local area networks (LANs), wide area networks (WANs), or the Internet and can enable location-independent data storage and retrieval.
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Branch: Information Technology Seminar title: INTERNET SCSI
iSCSI is one of two main approaches to storage data transmission over IP networks; the other method, Fibre Channel over IP (FCIP), translates Fibre Channel control codes and data into IP packets for transmission between geographically distant Fibre Channel SANs. FCIP (also known as Fibre Channel tunneling or storage tunneling) can only be used in conjunction with Fibre Channel technology; in comparison, iSCSI can run over existing Ethernet networks.
Organizations with changing data requirements, especially those requiring data storage security or disaster recovery, benefits most from the introduction of IP storage and iSCSI. Distributed intelligent services and automated allocation of storage resources via virtualization will become an integral part of the future evolution of iSCSI SANs.
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CONTENTS
1. INTRODUCTION
1.1. STORAGE BASICS
1.1.1. Direct Attached Storage (DAS)
1.1.2. Network Attached Storage (NAS)
1.1.3. Storage Area Networks (SANs)
2. FIBRE CHANNEL SAN (FC SAN)
2.1. LIMITATIONS
2.1.1. Total Cost of Ownership (TCO)
2.1.2. Operating distance
3. NEED FOR IP STORAGE
4. iSCSI UNDER A MICROSCOPE
4.1. iSCSI DEFINED
4.1.1. iSCSI Protocol
4.1.2. Convergence of Storage and Networking
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4.2.COMPONENTS OF iSCSI
4.2.1 Address and Naming Conventions
4.2.2 Session Management
4.2.3 Error Handling
4.2.4 Security
5 CONSTRUCTING A BASIC iSCSI SAN
5.2 iSCSI TARGET
5.3 NETWORKING INFRASTRUCTURE
5.4 iSCSI INITIATOR
6 BENEFITS
6.2 FIELD OF APPLICATION
7 CONCLUSION
8 BIBLIOGRAPHY
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Branch: Information Technology Seminar title: INTERNET SCSI
INTRODUCTION
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The function of a transfer protocol is to enable data transfer between host and target systems. Transfer protocols locate an appropriate target device, interpret application commands, translate them into commands understood by the target and move data between the device and system memory. Networking protocols define the way information is transferred between hosts and targets on a network. Depending on the configuration and application, data is transferred as either files or blocks. Storage protocols, such as SCSI (Small Computer Systems Interface) use block level data transfer to move information from one system to another. This results in data being transferred in a format native to storage devices rather than applications and operating systems.
File level transport across LANs, MANs and WANs has been common place for many years, however, block level transport has, until recently, been limited to short distances; typically local to one building or even rack enclosure. This changed with the creation of serialised SCSI architectures (most commonly fibre channel) which uses SCSI commands and protocols over a high speed serial connection, often using optical cabling. This allowed high speed, block level data transfers over distances as large as metropolitan areas, making SAN (Storage Area Network) technologies a usable (though costly) option for enterprise level businesses. For smaller organisations, fibre channel based storage solutions have proven too costly to implement.
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The iSCSI protocol merges the well established TCP/IP (Transport Control Protocol/Internet Protocol) networking protocol with the ubiquitous SCSI storage protocol and defines the rules for transporting block level data across TCP/IP based networks. iSCSI allows the transport of block level data without the need to implement costly, third party cabling. The principle of a SAN addresses many of the problems not previously made available to smaller businesses, such as scalability, disaster protection, data protection and, of course, capacity. In addition, as iSCSI is based on IP networking, storage over metropolitan and wide area networks is now possible
The iSCSI protocol merges the well established TCP/IP (Transport Control Protocol/Internet Protocol) networking protocol with the ubiquitous SCSI storage protocol and defines the rules for transporting block level data across TCP/IP based networks. iSCSI allows the transport of block level data without the need to implement costly, third party cabling. The principle of a SAN addresses many of the problems not previously made available to smaller businesses, such as scalability, disaster protection, data protection and, of course, capacity. In addition, as iSCSI is based on IP networking, storage over metropolitan and wide area networks is now possible.
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1.1. STORAGE BASICS
The Internet and related activities continue to expand, increasing the amount of data that needs to be stored. Businesses and other organizations require effective ways to store and maintain this data. Todayâ„¢s Technology market offers three basic options: Direct Attached Storage (DAS), Network Attached Storage (NAS) and Storage Area Networks (SANs).
1.1.1. Direct Attached Storage (DAS)
In its simplest form, DAS consists of a disk drive attached directly to a server. Data is transferred using SCSI (Small Computer System Interface) commands, the most common means of I/O communication between a computer and a hard drive. SCSI commands transfer data as blocks “ low-level, granular units used by storage devices “ as opposed to files, the most common means of transferring data over Local Area Networks (LANs).
There are a number of disadvantages to the DAS approach including high cost of management, distance limitations and limited scalability. In particular, in order to increase storage capacity, enterprises must purchase more servers. Furthermore, storage devices must be located close to the server since SCSI devices are designed to work over parallel cable with a maximum length of 12 meters. These limitations have driven the need for network storage.
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1.1.2. Network Attached Storage (NAS)
NAS is a file-based storage architecture with resources attached directly to the LAN. Storage traffic is transmitted over the LAN as well. Since it uses a familiar technology, NAS resources can be managed by existing IT staff with minimal training in storage management, which may reduce IT costs. Another benefit of NAS is flexibility “ since the storage unit(s) can easily be attached to the network. However, this is not a highly scalable option, since storage traffic can become very heavy and decrease the performance of the LAN.
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1.1.2. Storage Area Networks (SANs)
SANs are dedicated networks that connect servers to storage devices and transport storage traffic without burdening the enterprise LAN. Several factors help make SANs attractive, including performance, reliability, availability, scalability and ease of management.
Without the potential for centralized data management provided by SANs, redundant file copies can rapidly consume disk space, while multiple file
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versions cause reconciliation problems. In the absence of mature management tools, servers with high-demand applications and often-used data can become overloaded while others remain relatively idle. SANs, used in conjunction with managements tools, help reduce these problems. SANs are also highly scalable. Growing storage demands can be met by simply installing more storage and network resources.
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FIBRE CHANNEL SAN (FC SAN)
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Switches and other equipment in a SAN have historically communicated via a network protocol suite called Fibre Channel which allows SCSI commands to be transmitted via serial, rather than parallel, connections. The protocol also allows for relatively high throughput, transmitting data at 700 to 800Mbps in first-generation products and approximately twice that in second-generation products.
A Host Bus Adapter (HBA) connects the server to devices in the SAN. Typically, the server will have Ethernet and Fibre Channel connections to communicate with both the Ethernet LAN and the Fibre Channel SAN. The HBA serves the same purpose on the SAN side as a Network Interface Card (NIC) or network adapter servers on the LAN side.
2.1. LIMITATIONS
While Fibre Channel is a high performance transmission technology optimized for the same block storage format that storage devices use, it does have drawbacks:
2.1.1. Total Cost of Ownership (TCO)
The Total Cost of Ownership (TCO) for operating a Fibre Channel SAN, while lower than the DAS model, is still high. Since organizations vary widely in their storage needs, it is difficult to develop a set of assumptions for generating average cost figures. Cost is probably the biggest limitation of FC implementations. Although essentially limitless in the number of attached storage devices, the high cost of switch
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ports ($500 - $4000 per port) and FC HBAs ($500+ per HBA) make a high capacity FC implementation extremely costly.
Still, Fibre Channel is fairly new technology and many IT staffs have limited, Fibre Channel expertise. FC SANs are often complex in design and can require considerable expertise to configure and manage properly.Finding the necessary specialized personnel can be challenging and training is often not readily available. As a result, installing and maintaining a Fibre Channel network is typically difficult and expensive.
2.1.2. Operating Distance
The name fibre channel can be a little misleading as the physical interconnect is not limited to only optical fibre cabling; copper cabling is also used. Probably the biggest limitation for copper cabling in this environment is the distance over which information can be sent reliably without signal degradation. Because of this limitation, copper based fibre channel is used for relatively local configurations such as departmental setups. Optical cabling can, in most circumstances, transmit data reliably over distances of up to 10KM which allows data transfers over a metropolitan area which is of great use for disaster prevention and recovery.
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Although the theoretical limit for Fibre Channel is 10km, individual multi-mode fiber links used in Fibre Channel SANs may have a practical limitation of 250 to 500 meters. The storage ecosystem is evolving to where large organizations often SANs located far from the LAN, to provide geographical redundancy as part of disaster planning. This means even 10km may be increasingly inadequate.
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NEED FOR IP STORAGE
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Several factors are rapidly expanding worldwide storage requirements:
¢ E-mail
¢ E-Commerce
¢ A pervasive global economy
Over the past decade, many enterprises have seen a significant increase in the volume of data produced. The amount of data continues to increase, particularly in Web-based and e-Commerce environments.
E-mail impacts worldwide storage producing more data than is generated by new Web pages. These types of traffic are typically multimedia intensive. E-mail and Internet-related business/commercial transactions combined have caused a dramatic increase in storable data moving Internet Protocol (IP) networks. This traffic can potentially overwhelm existing backup methods.
A new method is needed to bring improved storage capabilities to IP networks and reduce limitations associated with Fibre Channel SANs. A rapidly emerging technology solution is Internet SCSI (iSCSI) or SCSI over IP.
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iSCSI UNDER A MICROSCOPE
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4.1. iSCSI DEFINED
Internet SCSI (iSCSI) is a draft standard protocol for encapsulating SCSI command into TCP/IP packets and enabling I/O block data transport over IP networks. iSCSI can be used build IP-based SANs. The simple, powerful technology can help provide high-speed, low-cost, long-distance storage solution for Web sites, service providers, enterprises and other organizations.
An iSCSI HBA, or storage NIC, connects storage resources over Ethernet. As a result, core transport layers can be managed using existing network management applications. High-level management activities of the iSCSI protocol “ such as permissions, device information and configuration “ can easily be layered over or built into these applications.
4.1.1. iSCSI Protocol
iSCSI describes a protocol for transmitting SCSI commands over TCP/IP. TCP handles flow control and ensures packets arrive at the destination in the correct order, while IP ensures data is routed to the correct destination/network. The iSCSI protocol links IP networking protocols with SCSI storage protocols enabling block level SCSI data and command transfer through the host initiator layers and through the stack layers of the target device. Naturally, this process takes place in both directions allowing data tobe transferred to and from iSCSI target and initiator machine.
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The initiator system, which is typically a server, will make an application request. These requests are converted to SCSI commands which are, in turn, transported into CDBs (Command Description Blocks) by the SCSI class driver. The SCSI CDBs are packaged into PDUs (Protocol Data Units) by the iSCSI device driver which appends additional information including the logical unit number of the target device. The PDUs are next sent to TCP/IP; TCP encapsulates the PDUs and IP adds routing information. Last, but not least, the network layer adds some final information and transmits the data, via Ethernet, to the target.
4.1.2. The Convergence of Storage and Networking
The emerging iSCSI protocol specifies a method for encapsulating SCSI commands in the TCP/IP protocol †the messaging protocol of the Internet. This encapsulation means that the Internet, or any TCP/IP network, can be used to carry storage traffic.
Storage and networking, therefore, are converging. An illustration of the stack is shown in the figure: iSCSI: The Layered View.
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iSCSI: The Layered View
4.2. COMPONENTS OF iSCSI
The iSCSI has four components:
¢ iSCSI Address and Naming Conventions.
¢ iSCSI Session Management.
¢ iSCSI Error Handling.
¢ iSCSI Security
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4.2.1. Address and Naming Conventions
As the iSCSI devices are participants of an IP network they have individual Network Entities. Such Network Entity can have one or several iSCSI nodes.
Fig. Model of Network Entities
An iSCSI node is an identifier of SCSI devices (in a network entity) available through the network. Each iSCSI node has a unique iSCSI name (up to 255 bytes) which is formed according to the rules adopted for Internet nodes. For example, fqn.com.ustar.storage.itdepartment.161. Such name has an easy-to-perceive form and can be processed by the Domain Name System (DNS).
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An iSCSI name provides a correct identification of an iSCSI device irrespective of its physical location. At the same time in course of handling data transfer between devices it's more convenient to use a combination of an IP address and a TCP port which are provided by a Network Portal. The iSCSI protocol together with iSCSI names provides a support for aliases which are reflected in the administration systems for better identification and management by system administrators.
4.2.2 Session Management
For the initiator to transmit information to the target, the initiator must first establish a session with the target through an iSCSI logon process. This process starts the TCP/IP connection, verifies that the initiator has access to the target (authentication), and allows negotiation of various parameters including the type of security protocol to be used, and the maximum data packet size. If the logon is successful, an ID is assigned to both initiator (an initiator session ID, or ISID) and target (a target session ID, or TSID). Thereafter, the full feature phaseâ€which allows for reading and writing of dataâ€can begin. Multiple TCP connections can be established between each initiator target pair, allowing unrelated transactions during one session. Sessions between the initiator and its storage devices generally remain open, but logging out is available as an option.
The iSCSI session consists of a Login Phase and a Full Feature Phase which is completed with a special command.
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The Login Phase of the iSCSI is identical to the Fibre Channel Port Login process (PLOGI). It is used to adjust various parameters between two network entities and confirm an access right of an initiator. If the iSCSI Login Phase is completed successfully the target confirms the login for the initiator; otherwise, the login is not confirmed and a TCP connection breaks.
As soon as the login is confirmed the iSCSI session turns to the FULL Feature Phase. If more than one TCP connection was established the iSCSI requires that each command/response pair goes through one TCP connection. Thus, each separate read or write command will be carried out without a necessity to trace each request for passing different flows. However, different transactions can be delivered through different TCP connections within one session.
Fig. iSCSI Write example
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At the end of a transaction the initiator sends/receives last data and the target sends a response which confirms that data are transferred successfully.
The iSCSI logout command is used to complete a session - it delivers information on reasons of its completion. It can also send information on what connection should be interrupted in case of a connection error, in order to close troublesome TCP connections.
4.2.3. Error Handling
While iSCSI can be deployed over gigabit Ethernets, which have low error rates, it is also designed to run over both standard IP networks and WANs, which have higher error rates. WANs are particularly error-prone since the possibility of errors increases with distance and the number of devices the information must travel across. Errors can occur at a number of levels, including the iSCSI session level (connection to host lost), the TCP connection level (TCP connection lost), and the SCSI level (loss or damage to PDU).
Error recovery is enabled through initiator and target buffering of commands and responses. If the target does not acknowledge receipt of the data because it was lost or corrupted, the initiator, a target, or a switch can resend the buffered data.
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So that error handling and recovery can work correctly both the initiator Each terminal must have a possibility to recover selectively a lost or damaged PDU within a transaction for recovery of data transfer.
Here is the hierarchy of the error handling and recovery after failures in the iSCSI:
¢ The lowest level - identification of an error and data recovery on the SCSI task level, for example, repeated transfer of a lost or damaged PDU.
¢ Next level - a TCP connection which transfers a SCSI task can have errors. In this case there is an attempt to recover the connection.
¢ At last, the iSCSI session can be damaged. Termination and recovery of a session are usually not required if recovery is implemented correctly on other levels, but the opposite can happen. Such situation requires that all TCP connections be closed, all tasks, underfulfilled SCSI commands be completed, and the session be restarted via the repeated login.
4.2.4.Security
Since iSCSI operates in the Internet environment, security is critically important. The IP protocol itself does not authenticate legitimacy of the data source (sender), and it does not protect the transferred data. ISCSI, therefore, requires strict measures to ensure security across IP networks.
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The iSCSI protocol specifies the use of IP security (IPsec) to ensure that:
¢ The communicating end points (initiator and target) are authentic.
¢ The transferred data has been secured through encryption and is thus kept confidential.
¢ Data integrity is maintained without modification by a third party.
¢ Data is not processed more than once, even if it has been received multiple times.
(The Internet Key Exchange (IKE) protocol can assist with key exchanges, a necessary part of the IPsec implementation.)
iSCSI also requires that the Challenge Handshake Authentication Protocol (CHAP) be implemented to further authenticate end node identities. Other optional authentication protocols include Kerberos (such as the Windows implementation), which is a highly scalable option.
Even though the standard requires that these protocols be implemented, there is no such requirement to use them in an iSCSI network. Before implementing iSCSI, a network administrator should review the security measures to make sure that they are appropriate for the intended use and configuration of the iSCSI storage network.
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CONSTRUCTING A BASIC iSCSI SAN
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The construction of a basic iSCSI SAN is actually a relatively simple process. For a basic configuration with basic functionality, no specialist hardware is required and, in many cases, freely available software can be used to run on both initiator and target machines. For more usable and secure implementations, it may be necessary to source more specialist hardware/software.
In order to create an iSCSI SAN, there are three main components which need to be considered:
¢ iSCSI Target(s)
¢ Networking infrastructure
¢ iSCSI Inititiator(s)
In addition to these primary components, there are other systems which can be implemented to enhance functionality, performance, security and/or manageability.
5.1. iSCSI TARGET
An iSCSI SAN will have one or more iSCSI targets and the responsibility of these devices is to house and make available the storage used within the SAN. For the majority of configurations, there are three approaches to creating an iSCSI target:
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¢ Modify an existing server.
Using target software from a variety of software vendors, it is possible to add iSCSI target functions to an existing server. This will allow a portion of the serverâ„¢s storage to be made available and have the server itself appear as an iSCSI target.
On the upside, this reduces the total cost of the solution as no additional hardware is required for the target, however, storage expansion within such a server is typically limited and performance can suffer dramatically if the server is performing other tasks.
¢ Specialist target appliances.
Many companies now offer specialist target appliance servers containing various storage capacities with a selection of redundancy features. These systems will be running a custom written software package providing iSCSI target functions and management utilities.
Such appliances do offer good iSCSI capabilities and a range of features which can be desirable depending on the architecture of the SAN, however, prices of such appliances can be relatively high and such systems are relatively inflexible with respect to feature upgrades and may not ideally suited to a specific environment/configuration.
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¢ Appliances built on generic hardware.
A significant feature of iSCSI is that it is not tied to a specific hardware technology. This means that iSCSI targets can be built on a variety of generic platforms whilst still maintaining full iSCSI compatibility. This allows for targets to be built using generic hardware meeting the exact feature requirements of virtually any implementation.
In addition to this flexibility, as the components are essentially generic, the cost of such target systems can be kept relatively low. The only specialist component in such a target would be the software providing the management and iSCSI target features and there are several companies who specialise in creating such software. As many of these software targets are based on NetBSD and Linux derivatives, the cost is often relatively low.
5.2. NETWORKING INFRASTRUCTURE
The networking infrastructure in the vast majority of iSCSI SANs will be standard 1Gb Ethernet. The configuration and complexity of the storage network will depend on its indented function and the features required, however, for many configurations, a simple 1Gb network switch with Cat5e cabling is sufficient for basic functionality. In the most basic of configurations (with only one target and one initiator) a simple cross-over cable between the two machines is possible.
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In larger organisations, where multiple sites might need access to the SAN, other network architectures may be used to communicate IP data such as dedicated lines, satellite links, VPN internet connections, etc.
5.3. iSCSI INITIATOR
The third component to an iSCSI environment is the iSCSI Initiator. The purpose of an iSCSI initiator is to allow a given machine access to the storage available in the iSCSI SAN. As with the targets, there are several approaches to creating an iSCSI initiator machine which will involve the use of either a hardware or software iSCSI initiator.
¢ Modify an existing machine.
It is quite possible to modify an existing system to act as an iSCSI initiator and is a very effective method of expanding the storage capabilities of an existing system which has an immediate need greater storage.
¢ Create a new machine.
The creation of a new machine to access data stored in an iSCSI SAN may seem excessive, but is a very viable solution for many scenarios. In many circumstances, it is advantageous to have a dedicated machine (or cluster of machines) accessing the iSCSI storage targets, acting as a gateway between the SAN and LAN interface
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In either situation, there are two initiator options enabling access to an iSCSI SAN; a hardware initiator or a software initiator.
A software initiator is little more than a piece of software which runs on a host system, communicating with an iSCSI SAN using a network interface attached to that host system. As the data arrives from, or is sent to, a given target, the data stream is decoded/encoded through this piece of software. This obviously has an impact on the host systems overall performance as the host systemâ„¢s CPU is responsible for decoding/encoding the data.
A hardware initiator typically takes the form of a PCI-X or PCI-E card and is designed to be installed in a standard PC based server or workstation system. Typically, such a card will have its own gigabit Ethernet interface to allow connection to the iSCSI SAN. A hardware initiator card will perform the same fundamental tasks as a software based initiator, however, the task of decoding/encoding is usually offloaded to a dedicated processing engine on the card. This is particularly advantageous when iSCSI connectivity is required on an existing, heavily used system.
Both software and hardware solutions are perfectly viable options and the intended functionality of the initiatorâ„¢s host system will determine which option will be more appropriate. If, for example, the system in question is to operate purely as a gateway between an iSCSI SAN and a LAN, a software initiator will usually be sufficient. If, however, an existing machine is being adapted to access an iSCSI SAN, the additional load on the CPU from a software initiator may be unacceptable, in which case, a hardware solution may be more appropriate
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BENEFITS
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By combining SCSI, Ethernet and TCP/IP, Gigabit iSCSI delivers these key advantages:
¢ Builds on stable and familiar standards “ many IT staffs are familiar with the technologies.
¢ Creates a SAN with a reduced TCO “ installation and maintenance costs are low since the TCP/IP suite reduces the need for hiring specialized personnel.
¢ Provides a high degree of interoperability “ reduces disparate networks and cabling, and uses regular Ethernet switches instead of special Fibre Channel switches.
¢ Ethernet transmissions can travel over the Global IP Network and therefore have no practical distance limitations.
¢ Scales to 10 Gigabit “ comparable to OC-192 SONET (Synchronous Optical Network) rates in Metropolitan Area Networks (MANs) and Wide Area Networks (WANs).
6.1. FIELD OF APPLICATION
iSCSI SANs are most suitable for organizations with a need for streaming data and/or large amounts of data to store and transmit over the network. This includes:
¢ Internet Service Providers (ISPs)
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¢ Storage Service Providers (SSPs)
¢ Organizations that need remote data replication and disaster recovery. For example, a high-technology company in San Jose remains susceptible to disaster if it uses a Fibre channel SAN. Original and backup data copies could be lost in the same earthquake due to distance limitations.
¢ Geographically distributed organizations that require access to the same data on a real-time basis. For example, work team members who need the latest project data without waiting 24 hours for traditional replication/backup/reconciliation procedures.
¢ Businesses and institutions with limited IT resources, infrastructure and budget. These organizations should look for iSCSI equipment that functions over standard Gigabit Ethernet Cat-5 copper cabling already in place in most buildings today.
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CONCLUSION
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As has already been detailed, iSCSI simply sends SCSI data and commands from a storage medium across an IP based network; the underlying storage technology is largely irrelevant to the functionality of iSCSI as is the physical network architecture and this is key to the future scalability of the iSCSI technology.
This independence from specific storage and networking architectures will allow the iSCSI technology to evolve and grow as both storage and networking technologies evolve. New drive technologies and capacities are already being introduced and iSCSI is ready to take advantage of the benefits they have to offer. Similarly, the introduction of 10Gb Ethernet is allowing iSCSI to fully capitalise on the higher performance of the latest drive technologies.
The future of low-cost, high-availability distributed storage is here today and it will only get better!
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http://studentbank.in/report-iscsi-downl...d-abstract
