In this article we closely examine the AlwaysOn Layers of Protection that are present in SQL Server
The AlwaysOn Availability Group feature in SQL Server provides disaster recovery and fault tolerance solutions, across various layers of infrastructure and components of application. This is one of the most important features to be introduced in SQL Server. It is because of this feature that the data from one instance is available across several systems in the server. This is of great use in large organizations with hundreds of systems. If any of the system stops working, the work won’t stop as the person can find their work on another system, using this feature.
This feature ensures that information is not just build using all the layers, but is also made available on all the layers. All of these layers have separate functions, and for efficient functioning of SQL Server instance, it is important for all layers to work together. A few of these layers are described below, to help guide you in your design thought process and subsequent implementation decisions. Collaboration and understanding is required among AlwaysOn layers for creating a successful solution for SQL Server.
- Infrastructure Level: This layer forms the first and the most basic of all layers; it is present at the server level and provides fault tolerance along with intra node network communication, which makes use of Windows Server Failover Cluster features for monitoring the health and coordinating failovers
- SQL Server Instance Level: This forms the second layer of protection. An instance of SQL Server that is installed in the Windows Failover Cluster is called SQL Server AlwaysOn Failover Cluster instance. These instances can failover to the relevant server nodes in WSFC. Nodes hosting the failover cluster instance are linked to a symmetric shared storage, which enable easy availability of data across systems.
- Database Level: The third layer across which the AlwaysOn operates and makes data available. A collection of databases that failover together, are contained in Availability Groups. These groups contain primary and secondary replicas, which are hosted by SQL Server instances on different nodes.
- Client Connectivity – The Fourth layer finally brings in the client applications, which have the ability to directly connect to a SQL Server instance network name or to a virtual network name. The later one is attached to Availability Group listener. In this layer it is possible to redirect connection requests directly to the relevant SQL Server instance and associated database replica.
The above mentioned layers of protection in AlwaysOn Availability Groups in SQL Server offers not just protection to the databases, but also makes it easier for the user to access these databases anytime. This is the feature that will not be found in earlier editions of SQL Server, as it was launched in 2012, compelling more and more SQL user to upgrade their editions.
In Midsized Firms, Despite the AlwaysOn Availability Group in Place, Possibility Of Some Amount Of Data Loss Exists in the Event of a Crash
The AlwaysOn Availability group feature is designed to allow business continuity. However in some cases, especially in mid sized firms, it implementation may not be optimal and chances of some data loss is always there. In such cases you should you use a recover sql tool like DataNumen SQL Recovery to bring back any missing records. This tool has the capacity to handle an array of data types and can even bring back indexes in perfect order. Further it has the dexterity to handle gigantic SQL files running into several gigabytes.
Alan Chen is President & Chairman of DataNumen, Inc., which is the world leader in data recovery technologies, including access recovery and sql recovery software products. For more information visit www.datanumen.com