Grid Computing - Guide to Cloud Computing for Business and Technology Managers - page 247

manually or automatically, to meet the changing needs and priorities of one's
business.
Virtualization has somewhat more of an emphasis on local resources,
whereas grid computing has more of an emphasis on geographically distrib-
uted interorganizational resources. Virtualization is a step along the way on
the road to utility computing (grid computing).
12.2.2 Cluster
The distinction between clusters and grids relates to the way resources are
managed. In the case of clusters (aggregations of processors in parallel-
based configurations), the resource allocation is performed by a centralized
resource manager and scheduling system. Also, nodes cooperatively work
together as a single unified resource. In the case of grids, each node has its
own resource manager and does not aim at providing a single system view.
A cluster is comprised of multiple interconnected independent nodes that
cooperatively work together as a single unified resource. This means all
users of clusters have to go through a centralized system that manages the
allocation of resources to application jobs. Unlike grids, cluster resources are
almost always owned by a single organization. These cluster management
systems have centralized control, complete knowledge of system state and
user requests, and complete control over individual components.
Actually, many grids are constructed using clusters or traditional parallel
systems as their nodes, although this is not a requirement.
12.2.3 Web Services
Grid computing also differs from basic Web Services, although it now
makes use of these services. Whereas the Web is mainly focused on com-
munication, grid computing enables resource sharing and collaborative
resource interplay toward common business goals. Web Services provide
standard infrastructure for data exchange between two different distrib-
uted applications, whereas grids provide an infrastructure for aggregation
of high-end resources for solving large-scale problems in science, engi-
neering, and commerce. While most Web Services involve static process-
ing and moveable data, many grid computing mechanisms involve static
data (on large databases) and moveable processing. These Web Services
will play a key constituent role in the standardized definition of grid
computing, since Web Services have emerged in the past few years as a
standard-based approach for accessing network applications. The recent
trend is to implement grid solutions using Web Services technologies, for
example, the Globus Toolkit 3.0 middleware. In this context, low-level grid
services are instances of Web Services (a grid service is a Web Service that
conforms to a set of conventions that provide for controlled, fault-resilient,
and secure management of services).