|Oracle RAC and Oracle RAC One Node on Extended Distance (Stretched) Clusters|
|Em 11g, Banco de dados, Oracle Database|
Oracle Real Applications Clusters (RAC) is a proven mechanism for local high availability (HA) for database applications. It was designed to support clusters that reside in a single physical datacenter. As technology advances as well as demands increase, the question arises whether Oracle RAC or Oracle RAC One Node over a distance is a viable solution.
Oracle RAC on Extended Distance (Stretched) Clusters is an architecture that provides extremely fast recovery from a site failure and allows for all nodes, in all sites, to actively process transactions as part of a single database cluster. While this architecture has been successfully implemented many times over the last decade, it is critical to understand where this architecture fits best, especially in regards to distance, latency, and the degree of protection it provides.
The high impact of latency, and therefore distance, creates some practical limitations as to where this architecture can be deployed. An active / active Oracle RAC architecture fits best where the two datacenters are located relatively close (<100km) and where the costs of setting up a low latency and dedicated direct connectivity between the sites for Oracle RAC has already taken place, which is why it cannot be used as a replacement for a disaster recovery solution such as Oracle Data Guard or Oracle GoldenGate.
Oracle RAC One Node completes the Extended Distance Cluster offering. While using the same infrastructure like Oracle RAC (i.e. Oracle Clusterware and Oracle ASM), Oracle RAC One Node is best used in environments or for applications that do not require the degree of HA or scalability that an active / active Oracle RAC database provides, but which benefit from an integrated and fully supported failover solution for the Oracle database.
As Oracle RAC One Node maintains only one instance during normal operation, it can also be used in environments, in which an insufficient latency prevents Oracle RAC to function optimally for example.
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