Very often applications need more computing power
than a sequential computer can provide. One way of
overcoming this limitation is to improve the operating
speed of processors and other components so that they
can offer the power required by computationally
intensive applications. Even though this is currently
possible to certain extent, future improvements are
constrained by the speed of light, thermodynamic laws,
and the high financial costs for processor fabrication. A
viable and cost-effective alternative solution is to
connect multiple processors together and coordinate
A computer cluster is a group of tightly coupled computers
that work together closely so that it can be viewed as a
Clusters are commonly connected through fast local area
Clusters have evolved to support applications ranging from
ecommerce, to high performance database applications.
Clusters are usually deployed to improve speed and/or
reliability over that provided by a single computer, while
typically being much more cost effective than single
In cluster computing each node within a cluster is an
independent system, with its own operating system, private
memory, and, in some cases, its own file system. Because the
processors on one node cannot directly access the memory on
the other nodes, programs or software run on clusters usually
employ a procedure called "message passing" to get data and
execution code from one node to another.
Cluster computing can also be used as a relatively low-cost
form of parallel processing for scientific and other applications
that lend themselves to parallel operations.
Customers invented clusters, as soon as they could not fit all
their work on one computer, or needed a backup.
The first commodity clustering product was ARCnet,
developed by Datapoint in 1977.
The next product was VAXcluster, released by DEC in
Microsoft, Sun Microsystems, and other leading hardware
software companies offer clustering packages.
A cluster is a type of parallel /distributed processing system
,which consists of a collection of interconnected stand-alone
computers cooperatively working together a single , integrated
a single or multiprocessor system with memory, I/O facilities,
generally two or more computers (nodes) connected together
in a single cabinet, or physically separated & connected via a
appear as a single system to users and applications
provide a cost-effective way to gain features and benefits
Start from 1994.
Donald Becker of NASA assembled this
Also called Beowulf cluster.
Applications like data mining, simulations,
parallel processing, weather modeling,
PC cluster deliver load balancing
Commonly used with busy ftp(file
transfer protocol) and web servers with
large client base.
Large number of nodes to share load.
Avoid single point of failure.
This requires atleast two nodes - a
primary and a backup.
Always with redundancy.
Almost all load balancing cluster are
with HA capability.
The components critical to the development of low cost clusters
3. Networking Components
4. Motherboards, busses, and other sub-systems
Computer clusters offer a number of benefits over
mainframe computers, including:
1. Reduced Cost
2. Processing Power
3. Improved Network Technology
1. Reduced Cost: The price of off-the-shelf consumer desktops
has plummeted in recent years, and this drop in price has
corresponded with a vast increase in their processing power
and performance. The average desktop PC today is many
times more powerful than the first mainframe computers.
2. Processing Power : The parallel processing power of a highperformance cluster can, in many cases, prove more cost
than a mainframe with similar power. This reduced price per
3. Improved Network Technology: Driving the development of
clusters has been a vast improvement in the technology related
networking, along with a reduction in the price of such
Computer clusters are typically connected via a single virtual
area network (VLAN), and the network treats each computer as
separate node. Information can be passed throughout these
with very little lag, ensuring that data doesn’t bottleneck
4. Scalability: Perhaps the greatest advantage of computer
scalability they offer. While mainframe computers have a fixed
processing capacity, computer clusters can be easily
requirements change by adding additional nodes to the
5. Availability: When a mainframe computer fails, the entire
However, if a node in a computer cluster fails, its operations
The cluster computing concept also poses three pressing
A cluster should be a single computing resource and provide
a single system image. This is in contrast to a distributed
system where the nodes serve only as individual resources.
The supporting operating system and communication
Mechanism must be efficient enough to remove the
It must provide scalability by letting the system scale up or
down. The scaled-up system should provide more functionality
or better performance. The system’s total computing power
should increase proportionally to the increase in resources.
The main motivation for a scalable system is to provide a
flexible, cost effective Information-processing tool.
If you are mixing hardware that has different networking
technologies, there will be large differences in the speed with
which data will be accessed and how individual nodes can
communicate. If it is in your budget make sure that all of the
machines you want to include in your cluster have similar
networking capabilities, and if at all possible, have network
adapters from the same manufacturer.
You will have to build versions of clustering software for each kind
of system you include in your cluster.
This is the most problematic aspect of cluster. Since these
machines have different performance profile our code will
execute at different rates on the different kinds of nodes. This can
cause serious bottlenecks if a process on one node is waiting for
results of a calculation on a slower node.
Our code will have to be written to support the lowest common
denominator for data types supported by the least powerful node
in our cluster. With mixed machines, the more powerful machines
will have attributes that cannot be attained in the powerful
There are a number of different kinds of network topologies,
including buses, cubes of various degrees, and grids/meshes.
These network topologies will be implemented by use of one
or more network interface cards, or NICs, installed into the
head-node and compute nodes of our cluster.
No matter what topology you choose for your cluster, you will
want to get fastest network that your budget allows. Fortunately,
the availability of high speed computers has also forced the
development of high speed networking systems.
Examples are :
10Mbit Ethernet, 100Mbit Ethernet, gigabit networking, channel
Web serving / searching (Google Search
ASPs (application service providers)
eMail, eChat, ePhone, eBook, eCommerce
E-commerce Applications (Amazon.com,
Database Applications (Oracle on cluster)
Cluster computing is no longer something which people see in
science fiction movies. This system of networking between
computers is not only necessary to continue to help business
become more efficient, but it also helps programs run more
quickly while also allowing people across the network cluster to
access the same programs, files, and information. It makes sense
to do this, doesn’t it? And since people like to communicate in
business, it makes sense that you cluster computing is only going
to become more popular as the economy rebounds and
businesses grow even more.
Clusters are promising
Solve parallel processing paradox.
New trends in hardware and software
technologies are likely to make clusters.
Clusters based supercomputers (Linux
clusters) can been everywhere !!
Clusters offer incremental growth and