Storage Area Network

SAN (Storage Area Network)

What is SAN (storage area network)?

A storage area network (SAN) is a dedicated network that provides access to consolidated,
block level data storage. SANs are primarily used to make storage devices, such as disk arrays,
tape libraries, and optical jukeboxes, accessible to servers so that the devices appear like locally
attached devices to the operating system. A SAN typically has its own network of storage
devices that are generally not accessible through the local area network by other devices.

A SAN does not provide file abstraction, only block-level operations. However, file systems built
on top of SANs do provide file-level access, and are known as SAN filesystems or shared disk file

Operating systems maintain their own file systems on their own dedicated, non-shared LUNs,
as though they were local to themselves. If multiple systems were simply to attempt to share a
LUN, these would interfere with each other and quickly corrupt the data. Any planned sharing
of data on different computers within a LUN requires advanced solutions, such as SAN file
systems or clustered computing.

Despite such issues, SANs help to increase storage capacity utilization, since multiple servers
consolidate their private storage space onto the disk arrays.

Common uses of a SAN include provision of transactionally accessed data that require high-
speed block-level access to the hard drives such as email servers, databases, and high usage file

Why Storage Area Networks?

A storage area network is better suited to large organisations and Government bodies
that have a disparate network, i.e. their offices may be located across the globe or over a
geographically wide area. This means that information is potentially stored across a wide range
of servers or other means of storage, and as a result it can be difficult to access information,
simply because it is not in a single place. As a result, finding and accessing the right information
can be extremely difficult and in many cases, impossible.

Information is generally regarded as an organisation’s ‘lifeblood’. It is critical because without
it most companies would not be able to function. More importantly, it should be seen as a
knowledge repository, in that it saves people replicating and researching, for example, a project
when perhaps someone in the organisation has already created a similar report or a similar
level of expertise.

Furthermore, most organisations have a storage requirement in so far as they need to retain
documents, files and other types of information and to be able to let it be accessed among
the users of the computer network. A storage area network is designed to separate storage
requirements from the organisations’ network and application servers. As a result, performance
is increased and people are able to access information faster and more easily and as a result,
potentially making them more efficient and productive.

SAN and NAS:

Network-attached storage (NAS), in contrast to SAN, 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.

Alternatives to Storage Area Networks

The main alternative to storage area network is Network Attached Storage.

At first glance, the differences appear to be few but it is imperative that you have a complete
understanding of both before making a decision to buy either.

In very simplistic terms, a NAS is less expensive than a SAN.

Storage area networks tend to be better suited to a large organisation with multiple locations
and servers. They tend to have a higher performance than a NAS and for a large organisation
where a great deal of information is exchanged, this can be critical.

• Benefits of Storage Area Networks over Network Attached Storage

• SANs tend to be faster than a NAS.
 SANs tend to be more expensive than a NAS. This is not because the storage is
expensive but the initial equipment can be prohibitive for some budgets.

• SANs offer very good data protection, i.e. it is difficult to access information unless you
have the authority to do so.

• SANs are more resilient, i.e. they are less likely to go wrong.

• SANs are better when huge amounts of storage are required.

Benefits of Network Attached Storage over a Storage Area Network

• NAS can be easily and inexpensively installed.

• NAS is cheaper than SAN.

• NAS requires less maintenance than SAN.

• NAS are easy to set up and use. An administrator is required for a SAN and requires
special training in order to maintain and configure the implemented SANs.

There are large a number of benefits why a storage area network or network attached storage
is better suited according to an organisation’s requirements, size and technical needs.

Both SAN and NAS have their merits and some would argue that their NAS system is extremely
fast and equally secure as a SAN. Both are extremely good solutions but it is advisable to speak
to a couple of credible suppliers that have expertise of both.

SAN infrastructure:

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.

Storage virtualization

Storage virtualization is the process of 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 physical location. This is implemented in modern disk arrays,
using vendor proprietary solutions. However, the goal is to virtualize multiple disk arrays from
different vendors, scattered over the network, into a single monolithic storage device, which
can be managed uniformly.


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