【正文】 eatest control and consolidation of resources necessary to execute the administrative function. Some control and resource consolidation is given up, however, due to the requirement of maintaining a remote data center environment with at least a minimal localized administrative presence. Remedial system maintenance requirements on the distributed system may include system updates that require a reboot of the puter, as well as tapebackup and storage duties. There may be additional localsite administrative requirements depending on the application or specific system being managed—you will have to decide what specific responsibilities are necessary based upon your technology application. Figure 4. Distributed hardware using remote administration 12 System A dministration As shown in the preceding figure, the centralized/remote administration model describes systems that are distributed to remote locations with all major administrative control remaining at the central location. As stated above, there now needs to be a data center presence in the remote or regional location to house the servers or storage units. This implies that you now incur the cost of the data center infrastructure, which includes the physical plant, floor space, power, wiring, HV/AC, and security ponents. If the technology application evolves to the point where this model no longer remains viable (that is, no longer meets the service level agreements) or is no longer cost effective, you may need to move to a distributed administrative model. In a distributed administrative model, the puting resources as well as the people resources are physically located at the remote location. This model is described in the next section. Centralized/Delegated Administration of Distributed Hardware The centralized/delegated administration model is shown in Figure 5. This model attempts to embrace the best of the centralized and remote administration models with all of their inherent features and benefits, yet also realizes some of the benefits of the distributed administration model. These benefits are achieved by pushing a relatively small and specialized subset of administrative tasks and responsibilities to the local branch offices and remote sites. As with the centralized model, the primary administrative function and administrative workforce reside at the corporate (central) data center—all administrative direction and control originate from this location. The centralized resources continue to manage the centralized, data centerbased work servers and services and also continue to remotely administer services across the work where possible, reasonable, and applicable. Certain circumstances dictate the need to distribute specific services, servers, and resources。 in these cases it may also be prudent and/or more efficient to allow some of the administrative tasks to be performed at the regional or remote locations. This is done by “delegating” very specific authority to the remote location resources. “Very specific authority” refers to a small subset of administrative rights and access that allow the remote administrators to perform specific, discrete tasks. Service Management Function 13 Figure 5 shows a possible application of the centralized/remote administration model. Figure 5. A centralized/delegated administration model Distributed Administration of Distributed Hardware Unlike the other models, distributed administration, shown in Figure 6, relies on full support resources located in remote sites or branch offices. Resources at remotely located sites perform the fundamental (although critical) support functions necessary to maintain the health, availability, and reliability of systems distributed to those sites. There may continue to be business reasons for maintaining systems that are distributed to remote locations. Some of these reasons may be related to performance, scalability, a specific type of application, or the cost or availability of work bandwidth that would support a centralized solution. 14 System A dministration Figure 6 shows an example of a distributed administration model for a pany with remote sites that are heavily populated with puter users. Figure 6. Completely distributed administration model As shown in Figure 6, puting and people resources are pletely distributed to the remote offices and regional sites. As a result, the pany may realize much better local site performance for specific technology applications. Specific Application Reasons for the Distributed Model Decision Here is an example of an application that affects the decision to distribute the environment (and subsequent administration thereof). Electronic messaging is one of the most critical applications that panies deploy to improve panywide productivity, munications (both internal and external), and puting efficiency for their businesses. Typically, early mainframebased messaging solutions were pletely centralized—both the hardware and the administrative support functions were centrally located in the pany’s data center. When personal puters and, eventually, serverbased, local area works (LANs) of personal puters became widely embraced and deployed, many panies decided to move the messaging applications from the mainframe to the serverbased works. This decision hinged primarily upon three factors: the unique richness available in the serverbased products and solutions, the cost benefits realized by downsizing applications from the more expensive mainframes to the less expensive servers, and the power that users realized by having a fullfeatured, localized, messaging client on their personal puter. For the most part, these early serverbased messaging solutions were, by necessity, distributed. Known by the type of message transport mechanisms they employed, these solu