Free Tutors on APPLICATION OF STORAGE NETWORKS in Web applications based upon the ‘travel portal’ case study

Free Tutors on APPLICATION OF STORAGE NETWORKS in Web applications based upon the 'travel portal' case study

This section uses the 'travel portal' case study to demonstrate the implementation of a so called web application. The case study is transferable to web applications for the support of business processes. It thus shows the possibilities opened up by the Internet and highlights the potential and the change that stand before us with the transformation to e-business. Furthermore, the example demonstrates once again how storage networks, server clusters and the five tier architecture can fulfil requirements such as the fault-tolerance, adaptability and scalability of IT systems.

 

	Representation Ø  Graphical user interface and interfaces to external Systems Ø  Converts user Interactions into applications calls Ø  Represents the returns of the applications
Applications Ø  Carries Out operations initiated by users in the Representation tier Ø  Reads processes and deletes dara that the data tier stores Ø  Stores applications data permanently  on block-oriented storage devices
Data Ø  Converts block oriented storage into tables(databases)or file systems Ø  Stores applications data permanently  on block-oriented storage devices

 

Figure 6.36 shows the realization of the travel portal in the form of a web application. Web application means that users can use the information and services of the travel portal from various end devices such as PC, PDA and mobile phone if these are connected to the Internet. The travel portal initially supports only editorially prepared content (including film reports, travel catalogues, transport timetable information) and content added by the users themselves (travel tips and discussion forums), which can be called up via conventional web browsers. Figure 6.37 shows the expansion of the travel portal by further end devices such as mobile phones and PDAs and by further services. To use the travel portal, users first of all build up a connection to the representation server by entering the URL. Depending upon its type, the end device connects to a web server (HTTP server) or, for example, to a WAP server. The end user only perceives the web server as being a single web server. In fact, a cluster of representation servers is working in the background. The load balancer of the representation server accepts the request to build up a connection and passes it on to the computer with the lowest load.  Once a connection has been built up the web browser transfers the user identifier, for example, in the form of a cookie or the mobile number, and the properties of the end device (for example, screen resolution). The web server calls up the user profile from the user management. Using this information the web server dynamically generates websites (HTML, WML or iMode) that are optimally oriented towards the requirements of the user. Thus the representation of content can be adjusted to suit the end device in use at

for the implementation of a three-tier architecture, since the clients (representation layer) communicate only with the application servers the time. Likewise, content, adverts and information can be matched to the preferences of the user; one person may be interested in the category of city tips for good restaurants,

whilst another is interested in museums. The expansion of the travel portal to include the new 'hotel tips' application takes place by the linking of the existing 'city maps' and 'hotel directory' databases (Figure 6.37). The application could limit the selection of hotels by a preferred price category stored in the user profile or the current co-ordinates of the user transmitted by a mobile end device equipped with GPS. Likewise, the five-tier architecture facilitates the support of new end devices, without the underlying applications having to be modified. For example, in addition to the con- ventional web browsers and WAP phones shown in Figure 6.37 you could also implement mobile PDAs (low resolution end devices) and a pure voice interface for car drivers.

 

	Representation Client (Web browser) Ø  Represents graphical user interface generated by the  Representation tier Ø  Passes on user interaction to Representation servers
Representation server (Web server) Ø  Generates graphical user interface to External systems Ø  Converts user interactions into application calls
Applications Ø  Converts block oriented storage into tables(databases)or file systems Ø  Reads ,Processes and deletes data that the data tier stores
Data Ø  Converts block oriented storage into tables(databases)or file systems
Storage Ø  Stores application data permanently on block- oriented storage devices

 

Figure In the five-tier architecture the representation layer is split up into representation server and representation client and the data layer is split into data management and storage devices All server machines are connected together via a fast network. Today primarily Gigabit Ethernet is used; in future InfiniBand will presumably also be used. With the aid of appropriate cluster software, applications can be moved from one computer to another. Further computers can be added to the cluster if the overall performance of the cluster is not sufficient. Storage networks bring with them the flexibility needed to provide the travel portal with the necessary storage capacity. The individual servers impose different requirements on the storage network:

• Databases

The databases require storage space that meets the highest performance requirements. To simplify the administration of databases the data should not be stored directly upon raw devices, instead it should be stored within a file system in files that have been specially formatted for the database. Nowadays (2003), only disk subsystems connected via Fibre Channel are considered storage devices. NAS servers cannot yet be used in this situation due to the lack of availability of standardized high-speed network file systems such as RDMA enabled NFS. In future, it will be possible to use storage virtualization on file level here.

• Representation server and media servers

The representation servers augment the user interfaces with photos and small films. These are stored on separate media servers that the end user's web browser can access directly over the Internet. As a result, the media do not need to travel through the internal buses of the representation servers, thus freeing these up. Since the end users access the media over the Internet via comparatively slow connections, NAS servers are very suitable. Depending upon the load upon the media servers, shared-nothing or  shared-everything NAS servers can be used. Storage virtualization on file level again offers itself as an alternative here.

• Replication of the media servers

The users of the travel portal access it from various locations around the globe. Therefore, it is a good idea to store pictures and films at various sites around the world so that the large data quantities are supplied to users from a server located near the user (Figure 6.38). This saves network capacity and generally accelerates the transmission of the data. The data on the various cache servers is synchronized by appropriate replication software. Incidentally, the use of the replication software is independent of whether the media servers at the various sites are configured as shared-nothing NAS servers, shared-everything NAS servers, or as a storage virtualization on the file-level.

 

In the first part of the book the building blocks of storage networks were introduced. Building upon these, this chapter has explained the fundamental principles of the use of storage networks and shown how storage networks help to increase the availability and the adaptability of IT systems.

As an introduction to the use of storage networks, we elaborated upon the characteristics of storage networks by illustrating the layering of the techniques for storage networks, investigated various forms of storage networks in the I/O path and defined storage networks in relation to data networks and voice networks. Storage resource sharing was introduced as a first application of storage networks. Individually, disk storage pooling, tape library partitioning, tape library sharing and data sharing were considered. We described the redundant I/O buses and multipathing software, redundant server and cluster software, redundant disk subsystems and volume manager mirroring or disk sub- system remote mirroring to increase the availability of applications and data, and finally redundant storage virtualization. Based upon the case study 'protection of an important database' we showed how these measures can be combined to protect against the failure of a data centre. With regard to adaptability and scalability, the term 'cluster' was expanded to include the property of load distribution. Individually, shared-null configrations, shared-nothing clusters, enhanced shared-nothing clusters and shared-everything  clusters were introduced. We then introduced the five-tier architecture – a flexible and scalable architecture for IT systems. Finally, based upon the case study 'travel portal', we showed how clusters and the five-tier architecture can be used to implement flexible and scalable web applications. As a further important application of storage networks, the next chapter discusses network back-up (Chapter 7). A flexible and adaptable architecture for data protection is introduced and we show how network back-up systems can benefit from the use of disk subsystems and storage networks.