Cloudware Technologies - Guide to Cloud Computing for Business and Technology Managers - page 311

Central management also allows to operate the distributed storage
systems at a lower cost. Moreover, different categories of data storage can
be organized in storage hierarchies (tier concept). This makes it possible to
implement an automated lifecycle management for data sets, from tier 0 with
the most stringent availability and bandwidth requirements to lower and
cheaper tier levels with a correspondingly lower quality of service. The data
can be migrated between these levels without affecting the service. By using
snapshots, even large data quantities can be backed up without a special
backup window. A further advantage of storage virtualization is that dis-
tributed mirrors may be created and managed in order to avoid service dis-
ruptions in case of malfunctions. Amazon, for instance, creates up to three
copies in different data centers when storing data.
15.2.4 Network Virtualization
Techniques such as load balancing are essential in cloud environments
because it must be possible to dynamically scale the services offered. The
resources are usually implemented as Web objects. For this reason, it is rec-
ommended to apply the procedures commonly used for Web servers: ser-
vices can be accessed via virtual IP addresses. Through cluster technology,
they realize load balancing as well as automatic failover in case of a failure.
By forwarding DNS requests, it is also possible to integrate cloud resources
into the customer's Internet namespace.
Network virtualization is also used for virtual local area networks
(VLANs) and virtual switches. In this case, cloud resources appear directly
in the customer's network. Internal resources can thus be replaced transpar-
ently by external resources. VLAN technology has the following advantages:
• Transparency : Distributed devices can be pooled together in a single
logical network. VLANs are very helpful when designing the IT
infrastructure for geographically disparate locations.
• Security : Certain systems that require particular protection can be
hidden in a separate virtual network.
On the other hand, VLANs involve more overhead for network administra-
tion and for programming active network components (switches, etc.).
15.3 Service-Oriented Architecture (SOA)
SOA introduces a flexible architectural style that provides an integration
framework through which software architects can build applications using a
collection of reusable functional units (services) with well-defined interfaces,