Down or Up the ? Is.
The main goal of a high availability solution is to minimize the impact of downtime. A sound strategy for this optimally balance business processes and SLA (Service Level Agreements) with technical capabilities and infrastructure costs.
With unplanned downtime, you must balance the time and effort needed to determine why outage occurred, what the current system state, and what steps are needed to recover from the outage.
Transactional activity on your primary SQL Server instance is synchronously or asynchronously applied t one or more secondary instances.
You can both measure the impact, and set recovery goals in terms how long it takes to get back in business.
Planning for Disaster Recovery
While high availability efforts entail what you do to prevent outage, disaster recovery efforts address what is done to re-establish high availability after the outage.
As much as possible, disaster recovery procedures and responsibilities should be formulated before and actual outage occurs.
High Availability with Microsoft SQL Server 2012
SQL Server provides a set of feature and capabilities that can help while keeping the cost and complexity low. AlwaysOn is a new integrated, flexible high availability and disaster recovery solution. It can provide data and hardware redundancy across datacenters.
An AlwaysOn solution can leverage two major feature of SQL Server 2012 for configuring at both the database and the instance level availability:
AlwaysOn Availability Groups greatly enhance the capabilities of database mirroring and helps ensure availability of application databases.
AlwaysOn Failover Cluster Instances (FCI) enhance the SQL Server failover clustering feature and support multisite clustering, which enables cross-data-center failover of SQL Server instances.
This article has established the baseline context for how to reduce planned and unplanned downtime, maximize application availability, and provide data protection using SQL Server 2012 AlwaysOn high availability and disaster recovery solutions.
For more: http://blogs.msdn.com/b/sqlcat/
http://www.microsoft.com/sqlserver/ : SQL Server Web site
http://technet.microsoft.com/en-us/sqlserver/ : SQL Server TechCenter
http://msdn.microsoft.com/en-us/sqlserver/ : SQL Server DevCenter