3. INTRODUCTION:
Super, Mainframe computers are not cost effective.
Cluster is a widely used term meaning multiple independent computers
combined to work in coordinated fashion to process applications into a
unified system through software and networking.
Clusters are typically used for High Availability (HA) for greater reliability
or High Performance Computing(HPC) to provide greater computational
power than a single computer can provide.
Whole computers working together as a unified computing resources
can create illusion of being one machine.
The term whole computer means a system that can run on its own, apart
from the cluster; each computer in a cluster is typically referred to as a
node.
Composed of many commodity computers , linked together by a high-
speed dedicated network.
5. CLUSTER CONFIGURATION:
High Availability Clusters:
These clusters are designed to provide uninterrupted availability of data or
service (typically web services) to the end user community. If a node fails, the
service can be restored without affecting the availability of the services provided
by the cluster, while the application will still be available, there will be a
performance drop due to missing node.
High availability clusters implementations are best for mission-critical
applications or databases, mail, file and print, web or application servers.
Load Balancing Clusters:
This type of cluster distributes the incoming requests for resources or content
among multiple nodes running the same program or having the same content.
Every node in the cluster is able to handle requests for the same content or
application.
Middleware mechanisms need to recognize that services can appear on
different members of cluster and may migrate from one member to another.
Almost all load balancing clusters are HA clusters.
This type of distribution is typically seen in a web hosting environment.
6. Parallel/Distributed Processing Clusters :
Parallel processing was performed by multiple processors in a specially
designed parallel computer. These are systems in which multiple processors
share a single memory and bus interface within a single computer.
These types of cluster increase availability, performance and scalability for
applications.
7. CLUSTERING METHODS:
Some clustering methods are:
Passive Standby:
Older method.
A secondary server takes over in case of
primary server failure.
Easy to implement.
High cost because the secondary server is
unavailable for the other processing tasks.
Heartbeat message.
8. Separate Servers:
Separate servers have their own disks. Data is continuously copied from primary to
secondary server.
High performance as well as high availability
Scheduling software needed for load balancing
High availability, Communication overhead
9. Shared nothing and shared Memory:
Reduce the communication overhead.
Servers connected to common disk.
Shared Nothing: common disks are partitioned into volumes, and each volume
owned by a single computer.
Shared Disk: Multiple computers share the same disks at the same time, so
that each computer has access to all the volumes on all of the disks.
11. Individual computers are connected by some high-speed LAN or switch hardware.
Each computer is capable of operating independently.
Middleware layer of software is installed in each computer to enable cluster operation.
The middleware provides a unified system image to the user, known as a single-system
image.
The middleware is responsible for providing high availability, by means of load balancing
and responding to failures in individual components. Following are the desirable cluster
middleware services and functions:
Single entry point
Single file hierarchy
Single control point
Single virtual networking (any node can access any other point )
Single memory space
Single job-management system
Single user interface
Single I/O space
Single process space
Checkpointing (saves the process state, recovery after failure)
Process migration (load balancing)
12. The last four items in the preceding list
enhance the availability of the cluster.
Others are concerned with providing a single
system image.
Implementation: Blade Servers
Is a server architecture that houses multiple
server modules (‘blades’) in a single chassis.
Used in data centres.
Increase server density, lowers powers and
cooling costs, ease server expansion and
14. CLUSTERS COMPARED TO SMP:
Both clusters and symmetric multiprocessors
provide a configuration with multiple
processors to support high-demand
applications.
Both solutions are commercially available.
SMP: the processing of programs by multiple
processors that share a common OS and
memory. Whereas , in clusters individual
systems are tied together.
The aim of SMP is time saving and of cluster
computing is high availability.
