SANs


Storage Area Network Definition: Storage Area Network (SAN) is a high performance network that connects storage devices and the back-end of servers. The deployment of a SAN allows the servers on a LAN or a WAN to access any number of storage devices.
 

 

SAN
 

Introduction
The main objective of a SAN is to facilitate the exchange of data between operating systems and storage elements. Components of a SAN infrastructure include communication infrastructure, storage elements, computer systems, and a management layer. The connecting elements of a SAN network include routers, gateways, hubs, switches and directors. A SAN removes restrictions on the number of servers that a storage utility can be attached to. The flexible networking of a SAN eliminates the need for physical proximity between the server and the storage devices. Benefits of a SAN include faster transfer of data to the intended destination with minimum utilization of server capacities, access for multiple hosts to several storage devices, independent storage speeds up applications and offers better availability, the management of stored data is easier and centralized and devices are more amenable to scalability. 

SANs have led to the development of several new methods for attaching servers to storage devices such as optical jukeboxes, tape libraries, and disk arrays.

The high-speed transfer of data via a SAN can occur in the following ways

1.    Connecting server/s to storage devices This is the most commonly used method and allows for the access of a storage device by servers either serially or simultaneously.
2.    Connection between servers SAN enables high-volume transfer of data between servers.
3.    Connection between storage devices Useful for moving data between storage devices without eating into server capacities which can then be utilized for other activities.

The need for SAN

The I/O bandwidth of the networks that were earlier used to connect the data storage devices and the processors was not commensurate with the capacities of the disk arrays and computers that utilized the data stored in them. The access to data is further complicated by the different database software run on different platforms. Managing different file systems and data formats requires trained manpower. The traditionally distributed storage has been a huge drain on management resources and inefficient as well in terms of capacity utilization of hardware resources. Scalability is also an issue when disk capacity is tied down to a single server or client. Sharing of data often requires creating duplicate copies, moving these copies slows down the LAN/WAN and often co-ordination between applications such as BI, CRM, and ERP that are spread over the entire organization becomes very difficult. 

SAN infrastructure

SAN topologies are predominantly developed using fiber channels. Fiber channel is an open technical standard developed for networking and is especially useful for handling storage communications as it offers flexible connectivity and fast access to data. Optical fibers are used for long-distance networking and copper cable links are preferred for shorter distances due to their lower cost. Fiber channels can support different protocols and a large number of devices, a quality very desirable in any networking solution.  

The American National Standards Institute (ANSI) has laid down the standards on which fiber channel networks are based. These standards define the manner in which data is to be moved across networks. The standards are exhaustive and cover physical interfaces, data encoding practices and protocols, data delivery methodologies, and common services. Fiber channels offer the advantage of a high level of hardware processing to ensure high performance. The serial data transport scheme used in a fiber channel can be implemented using simple cables and connectors. The information can be routed easily through switched networks. Since fiber channel transport layers are protocol independent, they enable the transmission of multiple protocols. Apart from being extremely flexible in its application, fiber channel delivers data at the rate at which the receiving application is able to handle; besides there is no loss of data. 

Storage

Storage devices commonly connected through SAN include disk systems and tape systems. Disk systems offer simple integration as the I/O control is centralized. Disk systems are classified as Just A Bunch Of Disks (JBOD) and Redundant Array of Independent Disks (RAID). Disks in a JBOD are treated as individual storage devices by the applications they are connected to. RAIDs are treated as a single device that has a higher fault tolerance. An array of disks can be made to behave as a JBOD or RAID depending upon the performance requirements of a SAN. Disk systems are preferred for online data storage because of their high performance.

Tape systems make use of tapes arranged serially; parallel arrangements are not possible. Tape systems consist of drives, autoloaders, and libraries. Tape drives connect the tapes to the devices and enable the reading/writing from and to the tapes. Tape autoloaders are tape drives that perform the function of auto backup; they are used for devices that generate a lot of data constantly. Tape libraries are autonomous sets of tape drives and autoloaders. They are used in situations where the storage capacity required is very high. Tape systems are used for offline storage because of their cost efficiency.

Benefits of SAN

One of the chief benefits of SAN is that it simplifies the network infrastructure and makes it easier to manage. This it does by means of consolidation, virtualization, automation, and integration. Consolidation aims at centralizing the storage to improve scalability, reducing infrastructure complexity, and increasing efficiency. Virtualization helps improve availability and reduces costs as it offers a holistic view of storage components. Automation of routine tasks allows the administrators to focus on critical tasks. Automation also improves responsiveness. Integration helps organization furnish users with the desired information in a more systematic manner.

A SAN makes information lifecycle management easier because of the integrated view of the data that it offers.

Perhaps the biggest benefit of a SAN is that it complements expensive business applications that demand instant and real-time information. ERP and CRM systems can fulfill their business promise only if the right type of data is made available at the right time to the right person. To this end, a SAN is most useful and appropriate.