High Availability of Database System

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Title : High availability of database system

High availability of database system, in which unplanned downtime is no more than seconds or only a relatively few minutes per year, is frequently a key objective in a data protection strategies, and one of the keystones of business continuity. However, an too much emphasis on high availability can lead to problems with data preservation (all the money goes into keeping the systems up and very little goes into preventing data loss when they go down), data responsiveness (fault-resilient storage often does not restore as quickly), and data confidentiality (all the money goes into keeping the systems up and very little goes to protecting data from unauthorized exposure). As a result, an organization may not meet its real data protection goals and probably will spend more than necessary for data protection.

Figure 1: High availability depends on the entire IT infrastructure

High availability depends on the entire IT infrastructure (Figure 1) and not just on the storage part of that infrastructure. For example, if a network is unavailable for any reason, data on disk array that an application access over that network is also unavailable, even if the disk array is working perfectly.

All application do not have same level of availability. However, for those application that need high availability, all of the relevant components of the IT infrastructure have to be tuned to the same relative level of protection. Otherwise, a weakest-link-in-the-chain problem exists.

Under normal circumstances the overall of IT infrastructure is unlikely to have been designed for high availability. High availability is a relative terms. There are actually higher and higher levels of availability, w...

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...d to user requests will allow you some time to switch systems. The bottom line is that you must plan the infrastructure needed to ensure that all components of your application are using the high availability features built into Application Server 10g and the Real Application Cluster Database 10g.

SQL Server 2008 has a number of high availability technologies; Windows failover clustering provides a protections against server failure; database mirroring and log shipping provide protection against site and database failure; and others. Selecting the appropriate high availability technologies requires matching to your organization’s availability needs and budget to the capabilities and requirements of different high availability technologies. Different technologies provided by SQL Server 2008 are design to give different levels of availability and data protection.

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