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SQL Server High-Availability with Virtualisation

By : Jerry Melnick
Nov 11, 2008

SQL Server associated applications and data are often mission-critical to the operation of a business. While protecting SQL Server and its databases is a top priority for IT departments, it’s often not enough. If the applications residing on SQL are not also protected, there is a risk that business operations will be disrupted. The complexity of SQL databases and applications creates further protection challenges.

Improving the availability of SQL Server and related applications involves eliminating likely downtime causes. At the highest level, downtime can be separated into two categories – planned and unplanned. Planned downtime is less disruptive since it can be scheduled for quiet periods, such as nights or weekends. Unplanned downtime, however, tends to occur at the worst possible times and can impact the business severely. Causes for unplanned downtime include hardware and software failures, data loss or corruption, and site outages.

There are a number of availability solutions for SQL Server out there for companies to choose from, and most of them fall into one of three categories – traditional failover clusters, virtualisation clusters and data replication solutions. All of these technologies rely on redundant servers to provide availability, and on a failover. While a failover is effective in bringing applications back online reasonably quickly, it does result in several minutes of application downtime, loss of in-process transactions and in-memory application data, and exposes the business to the risk of data corruption.

Local server redundancy and basic failover address the most common failures that cause unplanned SQL Server and application downtime. While data loss or corruption and site disruptions are less common downtime causes, they can result in much longer outages and pose a greater availability challenge. This is where the latest virtualisation technologies have an impact, making the protection of SQL Server and associated applications easier and more effective.

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