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TECH2TECH
Don't wait for a quake
Redundant systems: They're not just for disaster recovery anymore
by Margaret Mills and Bob Manning
What do you think of when someone mentions redundant systems? If you're like many people, you automatically see redundant systems as underutilized assets that cost too much money and don't deliver any benefit unless some type of disaster occurs. It's classic disaster recovery, right?
In the past—or with other data warehousing solutions—that would be absolutely right. But now, the Teradata Dual Active Solution is challenging traditional thinking about the way companies use redundant systems. In the past, companies have primarily purchased a second, redundant system as the ultimate insurance policy. It was the last stand against an unplanned outage, system crash or natural disaster. Redundant systems are an optional part of most computing platforms, including data warehousing, and are traditionally lumped together as part of an overall business continuity portfolio.
The problem with redundant systems has always been the cost-benefit equation. Make no mistake, installing a redundant system is the most expensive disaster recovery option available. The cost of duplicating and fully mirroring a primary system can simply become so unattractive from a financial standpoint that many organizations never seriously consider implementing a redundant system.
But what if that second system could deliver ROI? What if it could be designed and implemented as an active, productive system that is a permanent, working part of the data warehouse? Doing this can potentially increase revenue, improve customer satisfaction and influence customer behavior, all while providing near 100% availability.
The cost of disaster
Several Teradata customers are linking their business and high-availability strategies together to provide innovative applications that distinguish them from their competitors. Here are a few examples:
> Intelligent inventory/supply chain applications that not only predict and detect stock outages, but actually reroute drivers already on the road to pick up or drop off additional goods.
> Customer service applications that detect when a flight, bus or train will be delayed and automatically reroute or rebook passengers before they miss their connections.
> Subscription services that not only provide customers with historical data but also real-time data, allowing for immediate analysis of market conditions compared with previous trends.
> Real-time call detail recording analysis to detect dropped calls and generate proactive customer service before the customer has the chance to call and complain.
Sounds great, doesn't it? But we've been hearing about active data warehousing and real-time applications for years.Why is this different, and what do redundant systems have to do with it? All of these applications are vital to their respective companies. They are all mission-critical applications that influence customer behavior, customer satisfaction and company revenue.
There could be a separate debate about how to define mission-critical applications, but in reality, they can be easily defined. Financial value is the ultimate measurement tool in business. The criteria for determining whether an application is mission-critical or not depend on the revenue loss (or other costs) to the business should the application become unavailable for some period of time. These costs should be readily apparent and easily measured. The applications just described have apparent short-term financial impact on the organization, whereas traditional data warehouse applications are less time-sensitive and/or do not directly impact finances.
A sturdy structure
Having established the mission criticality of these applications, we are at the all-too familiar crossroads of how to handle availability.With mission criticality seeping into the data warehouse, availability issues must be addressed in a way that provides a return on investment, while ensuring disaster recovery and business continuity.
Teradata's Dual Active Solution is specifically designed to meet the needs of customers who are pursuing and developing mission-critical, active applications for the data warehouse. Since these applications will require a higher level of availability than a single system alone can provide, as well as disaster recovery, customers need something other than a redundant system as an insurance policy. The Teradata Dual Active Solution "activates" the secondary system so you can utilize it for daily production.
This is a very new and exciting way to think about redundant systems. You not only have the disaster recovery you need, but you can also achieve near-100% availability for both planned and unplanned downtime for applications available on both systems. Because the second system is "active," it can also have a positive ROI just like the primary system—something previously unachievable with a "passive" system acting only as an insurance policy.
In addition to providing a positive ROI, increased availability and reduced downtime, the Teradata Dual Active Solution supplies a number of capabilities and is flexible in ways that redundant systems have never been before.
With this new solution, the requirement to mirror the entire database or platform is eliminated—although it's still an option for those customers who seek 100% redundancy. Most early adopters have estimated their mission-critical data to be between 30% and 50% of their total data. By controlling availability for only those mission-critical applications, they experience significant cost savings over a traditional redundant system.
Each year, planned downtime represents approximately 60% to 75% of the total downtime associated with a computing platform.With the secondary system always up and running, it can assist in eliminating planned downtime and boosting availability—a boost that can be another financial benefit to the business.
In addition, because the system is "activated," it also provides additional processing power that helps to smooth peak workloads on the primary system. Customers have the ability to prioritize certain users, applications and even queries so they will benefit from the power of the secondary system.
Engineered to survive
We've talked about the benefits of a dual active system and the Teradata Dual Active Solution, but making this vision a reality is not as simple as just plugging in another box and linking it back to the primary system. Implementing it means thinking differently about how you do business, how you develop applications and how you handle platform and configuration issues.We have seen some customers choose to invest in the Teradata Dual Active Solution architecture as part of the business case for these new active applications, but other companies choose to "grow into" the dual-active architecture through a planned growth program as part of their data warehousing strategy.
The Teradata Dual Active Solution comprises traditional Teradata hardware and the Teradata Database. The solution also includes Teradata Query Director Software and customized services to implement the solution. Teradata Query Director Software provides session routing and failover for users and applications. Teradata Professional Services establishes the necessary data synchronization, monitoring and management capabilities.
Let's take a look at each of these areas in more detail.
Although there are many ways to implement a Teradata Dual Active Solution, a typical solution starts with an evaluation of customer requirements and a determination of what data and applications the Teradata Dual Active Solution should support.When identifying applications that will be included on the secondary system, it is important to understand the following:
> Data requirements— Which tables and how much historical data are needed to support that application?
> Recovery point objective— How current does the alternative system's data need to be when an outage occurs? Do you need all historical data, or just a subset?
> Service level requirements— What kind of "uptime," performance and response time do you need?
> Recovery time objective—What is the length of time between an outage occurrence on the primary system and application availability?
Next, we consider how to "activate" users on the second system. Just having data available on a second system isn't sufficient. Teradata Query Director software provides a number of ways to meet this challenge. This software is able to route user and application sessions to one or more Teradata systems. In the normal situation where all systems are available, it routes each session, based on user ID and/or account string, to a Teradata system based on a number of decision criteria. In situations where the data required for that user is only available on a specific system, Teradata Query Director can force a particular user/application onto that system.
It also has the capability to reroute users and applications based on failure codes. As a result, application requests can be rerouted to the alternative system—to which the user and application are already connected—in case of a failure. Teradata Query Director software offers a number of possible routing and management scenarios. Ultimately, each customer will define his or her own rules and the implementation will be customized to reflect the customer's specific desires.
Data synchronization is a key issue when dealing with any redundant system environment, and the Teradata Dual Active Solution is no exception. In a datawarehousing environment, up to 95% of all data remains static once loaded to the data warehouse. For these tables, the most efficient method of synchronization is a dual-loading process, where both the primary and secondary systems are loaded with the same data simultaneously. In addition to providing the most resource efficient method to load both systems with synchronized data, dual loading has the added benefit of allowing data loads to continue to each Teradata system, even when the other system is out of service for planned or unplanned reasons.
For those tables that will see some change occur after they are loaded into the data warehouse, there are other synchronization options that are more efficient. Synchronization decisions need to be made for each table that will reside on the secondary system.
Teradata Professional Services works with each customer to select the most appropriate synchronization method. The chart in figure 1 highlights some of the possible synchronization methods and their characteristics.
The final component of the Teradata Dual Active Solution involves system monitoring, administration and control. A Professional Services customized software layer that resides between the two systems (primary and secondary) can be implemented to handle these functions. These applications monitor the system for outages, as well as the data synchronization processes and Teradata Query Director software. If a planned or unplanned outage happens, the system triggers a change in state. The operational control level makes the changes necessary to the system to account for the outage and continue to handle workloads. Finally, administrative controls allow you to perform administrative tasks, further customize certain aspects of the system and perform traditional system management.
The new Teradata Dual Active Solution potentially adds a new component to data warehousing—the ability to deliver a mission-critical platform for innovative applications. Many of the technological obstacles to activating a second system have been overcome, and today there are Teradata customers who benefit from an enhanced data warehouse. As is often the case with technological advancements, the remaining challenges often have more to do with internal culture, thinking and attitudes than with whatever technological obstacles remain.
Margaret Mills, Teradata senior product manager, has developed and implemented multi-platform, multi-vendor and multisize business continuity plans, including Recovery Center solutions and environments. Margaret can be reached at margaret.mills@teradata-ncr.com.
Bob Manning, Teradata Programs manager, supports sales teams by providing insight about Teradata products, services and solutions. Bob can be reached at bob.manning@teradata-ncr.com.
© Teradata Magazine-June 2004
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