PCA and PRA Part 1

PCA and PRA: the corporate weapon against computer disasters. Few companies today can dispense with them to the point that in many cases IT inability to deal with a computer problem can be fatal. A study by the American consulting firm Eagle Rock, 40% of companies with an interruption of 72 hours of their IT and telecommunications resources do not survive a data disaster. That is why more and more companies of all sizes strive to implement a disaster recovery plan or an IT business continuity plan.

Over time, the meaning of these two terms has evolved. Historically, the continuity plan clung to analyze the potential impact of a disaster or failure on the company’s business and defining the means and procedures to be implemented to limit the consequences. The recovery plan was interested meanwhile IT aspects of the PCA.

For IT professionals, the terminology has evolved increasingly BCP describes all means to ensure business continuity applications, that is to say, to ensure high availability of the applications (which implies the impossibility of stopping these applications even in case of disaster on a site). The PRA meanwhile describes all the means and procedures designed to ensure a rapid and orderly resumption of production after an unexpected shutdown (for example related to a technical failure, or energy, human error or a natural disaster) . The difference between the two approaches tends to be limited to a difference in terms of infrastructure downtime and disaster recovery applications.

PCA: ensure high availability of applications

As part of a PCA, the company ensures define architectures, means and procedures necessary to ensure high availability of infrastructure (data center, servers, network, storage) supporting the implementation of enterprise applications. The objective is to ensure that whatever the situation, the infrastructure put in place ensure users uninterrupted service.

In general, a PCA implementation requires the establishment of facilities between several redundant data centers and operating jointly so that in case of component failure at the primary site, the relay automatically made by the secondary site.

Typically, such an architecture implies the establishment of a scheme guaranteeing consistency on storage arrays between the primary site and the secondary site. One example that allows a solution like EMC VPLEX as the latest generation of berries VSP Hitachi G1000. It is also possible that technology GeoCluster NetApp or HP (3Par). These two technologies actually provide transparent data replication between two or more sites and allow simultaneous write access to data on all sites. Coupled with orchestration and virtualization solutions, where to failover software technologies (Oracle RAC, SQL Server Failover Cluster …), they allow automated switches applications of a data center to the other in case of failure on the primary site.

Note that all enterprise applications are not necessarily concerned with the implementation of a BCP, just because some are not deemed critical and can tolerate a stop, or a possible loss of data. This criticality is defined collaboratively with the business to determine what the scope of the PCA and which applications will be affected by a “simple PRA”. It should also be properly sizing the infrastructure for failover to the secondary site does not affect the performance too. In the case of an architecture in active / active mode, production is indeed divided between the two data centers of the company, so a disaster on one of them translated mechanically by a decrease half the processing capacity available, thus potentially a performance degradation of the surviving infrastructure.

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