Storage area network

STORAGE AREA NETWORK

Submitted by,

Neha agarwal

DEFINITION

A SAN (Storage Area Network) is a network designed to transfer data from servers to targets, and it is alternative to a directly attached target architecture, or to a DAS architecture

Additional definitions of a SAN imply that the SAN should also be highly performing, and should be such to enable storage devices to communicate with one another and with computer systems

SAN ARCHITECTURE

Storage is accessed at block level not at file level

Very high performances

Storage is shared Good management

tools Interoperability

issues

Storage Area Network (SAN)

DatabaseServers

BlockStorageDevices

Fibre Channel

SAN

Clients

LAN

DIFFERENT TECHNOLOGIES

Multiple technology can be used when building a SAN; traditionally the dominant technology is Fiber Channel, but IP based solutions are also quite popular for specific applications

The concept of SAN is also independent from the devices that are attached to it. Can be disks, tapes, RAIDs, file servers, or other

SAN AND NAS: NETWORK AND NODE

SAN vs NAS: while a SAN is a network connecting storage subsystems, the NAS is a storage subsystem, making use of a general purpose network.

The SAN is an extension of the disk channel outside the server, while the NAS is a disk subsystem connected to the servers, in most cases via an IP network.

HARD DRIVES The basic storage element is an Hard Drive. They

are made into complex devices composed of platters, heads, cylinders and tracks

File systems arrange files into sectors so that they can be stored and retrieved

The File system usually deals with clusters of blocks and uses a FAT (File Allocation Table) to map a file to the sectors

SAN VIRTUALIZATION

As it has been found quite complex, virtualization concept came into picture for the sake of effective and efficient management of SAN. Virtualization can be defined as an abstracted management of huge amounts of equipment and data. Virtualization takes all diverse and large complex storage devices and makes them appear as one Hugh volume.  Presently there are three proven methodologies for achieving SAN virtualization in the market.

TYPES OF SAN VIRTUALIZATION

Host-based virtualization - This methodology requires a control software program on every server that accesses the SAN. The main benefits out of this are easy installation and access.

Storage-based virtualization - It works in a homogeneous hardware environment, i.e., everything has to be from the same vendor.

A SAN appliance virtualizes storage and has the effect of converting various storage devices into one big disk. This big virtual disk stores terabytes of data that can allocate storage to different applications quickly and painlessly.

SAN SUPPORTED TOPOLOGIES: POINT TO POINT

Point to point is the simplest topology for very limited connectivity needs

It guarantees in order delivery and full bandwidth access

The application can handle any multipath connectivity to a set of disks in case this is provided, since no other elements are present in this topology

TX TX

RX RX

SAN SUPPORTED TOPOLOGIES: ARBITRATED LOOP Designed to scale to a limited number of nodes (up to 127) Low cost (no interconnecting devices needed) Arbitration protocol is designed to manage media sharing

across nodes; may be disruptive when a node gets added/removed from loop and loop initialization protocol kicks in

A arbitrating hub can be used instead of a distributed protocol

Each node can be a server or a storage device

SAN SUPPORTED TOPOLOGIES: SWITCHED FABRIC

In a switched fabric topology, switching element get added to the nodes to allow interconnections via point-to-point links

Extended number of devices (potentially thousands) and greater distances can be achieved

Scalable, robust and reliable architecture, but the cost of the interconnection devices adds on

Switched Topology

BlockStorageDevices

Fibre Channel

SAN

SUMMARY

What is a SAN Basic Building Blocks of a SAN A zoom into the Storage Architectures SAN elements and architecture FIBRE CHANNEL

FIBER CHANNEL AND THE OTHERS

The Fibre Channel (FC) is used to develop practical, inexpensive, means of quickly transferring data between workstations, supercomputers, desktop computers, storage devices, displays and other peripherials.

Long cable length up to 10 km. Transfer speeds up to 2 gbps. Data must be sent through frames. Used as a backbone for most commercial

networks

SUMMARY

What is a SAN Basic Building Blocks of a SAN A zoom into the Storage Architectures SAN elements and architecture Basic Protocols and Mechanisms Advantages and disadvantages

SAN ADVANTAGES SAN Architecture facilitates scalability - Any number of

storage devices can be added to store hundreds of terabytes.

Sharing SAN is possible - As SAN is not directly attached with any particular server or network, a SAN can be shared by all.

SAN provides long distance connectivity - With Fibre channel capable of running up to 10 kilometers, we can keep our data in a remote, physically secure location. 

SAN is truly versatile - A SAN can be single entity, a master grouping of several SANs

SAN DISADVANTAGES

SANs are very expensive as Fibre channel technology tends to be pricier and maintenance requires a higher degree of skill .

Management of SAN systems has proved to be a real tough one due to various reasons. Also for some, having a SAN storage facility seems to be wasteful one.

  Also, there are a few SAN product vendors due to

its very high price and very few mega enterprises need SAN set up.

CONCLUSION

SAN is literally a separate network devoted entirely to storage. Almost all SANs communicate and connect to servers via a Fibre channel host adopter card and switch.