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.
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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.
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