Every new version of SQL Server brings with it new tools and features for database administrators (DBAs), developers, and architects, for them to be able to provide an effective solution to the end users in a simpler and more efficient manner. The terms effective and efficiency can be measured in a technical perspective as High Availability (HA) and Disaster Recovery (DR).

Let's assume that a world-wide retailer's CTO has been tasked to provide high availability for their mission-critical back-end systems that are built upon SQL Server technologies. This is a major task for DBAs to implement an HA solution on a SQL Server data platform, and for developers to ensure that underlying application architecture is HA-aware to take advantage of mission-critical features from SQL Server technologies.

SQL Server High Availability features include failover clustering, database mirroring, log shipping, replication, backup and restore strategies. The solution must fit within the company's budget, keeping up the scalability, and should reduce degradation in performance. When it comes to the disaster recovery solution, it may not be possible for the primary and secondary site's hardware to be the same, such as fewer hardware resources, limited storage capacity, or data center limitations. It may be acceptable to the business in terms of costing, but when a disaster strikes, the damage will be irrecoverable. All such out of the box limitations must be avoided, or reduced, to keep up the mission-critical applications always online.

The most critical aspect of any high-availability solution is designing a failback (quick recovery of data) strategy, that is, the application must be designed to direct the connections to the available instance when the SQL Server instance fails over to secondary server in a seamless manner. Though SQL Server is an out of the box disaster recovery tool, many of them are limited to traditional methods of backup and restore functionality that are time consuming during a recovery event. So, the new trend in the industry is to replace the existing older backup and restore policies, taking advantage of hardware capabilities as a DR solution. This requires server-class hardware and standardization on same hardware to take such advantage, but still lacks the quicker data recovery strategy.

To overcome the point-in-time data recovery problems, an enterprise-level HA solution is essential. This is where SQL Server provides such a business value proposition for the end users.

To be a competent DBA, developer, or architect, a firm grasp of tools and features is highly essential. The internal architecture of SQL Server provides a greater deal on HA and DR capabilities. Similarly, this book can be helpful as a roadmap when you work your own way to succeed in implementing high availability features and technology, with the help of SQL Server 2008 version.

A giant leap starts with a small step. Similarly, to begin with HA and DR solution implementation, the underlying architecture of SQL Server 2008 (and higher) will provide a good foundation to your existing data platform. This book covers the key aspects of important features of SQL Server high availability along with a tour on best practices implementation. The book starts with a clear understanding, to enable the readers to understand how the SQL Server security mechanism works and how tightly it is integrated in the Windows domain.

It covers the itemized measures to take on the out-of-SQL Server environment such as understanding the importance of windows domains, domain users, and the security measures to benefit from the latest version of SQL Server. Then it cruises through the implementation of clusters with a best example scenario that will help users set up a multi-instance SQL Server failover cluster with a specific difference between single-instance and multi-instance SQL Server failover cluster nodes. The first chapter touches on Windows Hyper-V technology, specific component configuration in a failover cluster environment, and advantages of multi-instance failover cluster over the single-instance failover cluster. This is a best illustration on how a road map should begin and helps design a high-availability solution.

So, when it comes to mission-critical support for your SQL Server data platform, the pool of SQL Server technologies resources is out there. But keep in mind that the advantage of SQL Server can be implemented in various configurations for different purposes, and so finding a single resource with everything you need may prove difficult. In any case or scenario, this book will help users through the comprehensive levels of HA and DR implementation for their data platform needs.

Satya Shyam K Jayanty (SQL Server MVP)

Principal Architect & Director D Bi A Solutions Limited