Oracle 10g RAC Versus DataGuard For High Availability
[courtesy: http://www.iheavy.com]
Oracle has two very different technologies, each with it's own strengths and weaknesses that implement high availability solutions. In choosing between the two technologies, it's important to factor in the relevant risks, both small and large, to put the entire picture into perspective.Two Alternatives
RAC or Real Application Clusters, is essentially an always-on solution. You have multiple instances or servers accessing the same database on shared storage in your network. With existing technology limitations, in practical terms, these different servers must be on the same local network, in the same datacenter.
Oracle's DataGuard technology, formerly called Standby database in previous versions, provides a rolling copy of your production database. The standby database is started in read-only mode, constantly receiving change data, sent over from the production database, keeping it always in sync at all times, and at most only a few minutes behind. Were the production server to fail, that server could take over in less than the time the DNS change or IP swap would take. What's more the standby copy can be at another datacenter, or on another continent!
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