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The benefits of thin replication for disaster recovery

Offering replication to a disaster recovery site is tricky business: The purchase of extra storage hardware can be prohibitive, and setting up an efficient system is a tedious process. But a new technique, thin replication, can lower the bar to disaster recovery replication.

Solution provider takeaway: Learn about the benefits of thin replication, which could be the right answer for customers looking for a simple, low-bandwidth replication solution for disaster recovery.

Usually, when a customer asks a reseller to provide a solution for replication to a disaster recovery site, the reseller thinks, "Well, that's good news and bad news." The good news is that the customer will need extra storage. The bad news is that the extra storage may break the budget, and the customer may have to put the purchasing process on hold to find additional funds.

Beyond potential budget problems, there's the technical difficulty: Setting up an efficient and easy-to-use replication topology is tedious and time-consuming. Managing and implementing replication via products such as SRDF and TrueCopy/Universal Replicator is a very complex undertaking; it's also costly and difficult to adopt without some sort of professional services engagement.

Despite both of these problems, a replicated copy of data for disaster recovery is no longer a "nice to have" for most data centers -- it's a requirement. So how can a solution provider address the need for replication, have a satisfied customer and live to tell the tale?

Up until recently, there really was no easy answer. But now, next-generation replication techniques that will make life easier for resellers and their customers are on the way. Companies like Compellent Technologies and 3PAR are leveraging thin provisioning capabilities into their replication offerings. Of these two companies, Compellent has gone the furthest by providing advanced quality of service (QoS) and bandwidth shaping. Armed with these "thin replication" products, you'll no longer have to spend days upon days at your customer's site configuring the replication topologies with complex FCIP interconnection schemes, full disk-based copies, little bandwidth control and cumbersome management interfaces.

What makes thin replication thin?

Traditional SAN replication involves a significant planning cycle to determine which protocol to use, acquire the needed conversion hardware and decide how much bandwidth is required. And the actual implementation is complicated because those scripts have to be written, tested and fine-tuned. Finally, ongoing management is a challenge, since no data center is static; changes to the application infrastructure will mean changes to the replication environment and a call to the storage reseller for support.

One of the benefits of a thin replication solution is that it provides -- unlike traditional replication techniques -- the ability during the initial replication phase to replicate only the data that has been written to a given area rather than the entire allocated amount of capacity. Most other techniques require a block-for-block copy. For continual replication, only the changed data sets are replicated to the alternate location(s). This gives your customer the ability to conserve costly bandwidth segments that would normally be overtaken by replicating needless amounts of allocated but unused capacity (white space). The target systems can be deployed with a diminished capacity, saving customer budget and allowing you to sell only the bandwidth and storage your customer needs at the time they need it.

Thin replication reduces the replication process to just a few mouse clicks. It's no longer necessary to undertake large scripting efforts to automate replication; instead, the process is driven through simple and easy-to-create replication templates. You can install the solution without needing office space while you make it work.

Quality of service

Most replication techniques don't enable you to scale bandwidth prior to installation, though it can be accomplished via integration or added software functions. Another benefit of thin replication is the variety of unique tools that allow you to model the customer's bandwidth and provide a QoS level, capabilities missing from other replication techniques. Being able to look at your customer's source data and model the required replication bandwidth up-front, before they procure the bandwidth and/or target systems, means you can sell only what your customer needs for its disaster recovery replication.

In addition to enabling users to estimate the amount of bandwidth a data center will need in the future, thin replication provides the ability to throttle bandwidth usage throughout the day and monitor that bandwidth usage over time. This gives your customer the flexibility to replicate data without burdening business operations during peak hours.

Even if your customers don't start with replication on the initial installation of these products, these tools let them continuously model their data sets over time, and when they are ready to implement replication, they can provide you with all the necessary data to do so properly. In a typical scenario, you would need to use host-based tools along with array monitoring processes to determine the up-front and ongoing change rates. The QoS offered in thin replication allows storage administrators to change a number of very useful parameters, such as:

  • Scaling replication bandwidth up and down during peak and off-peak hours to ensure adequate usage of the links based on customer SLAs.
  • Giving priority to one data set over another based on the business-critical nature of the data contained within a given volume. This allows an administrator to provide, for instance, a higher spec to an SAP volume than a file server one.

On the topic of QoS, legacy replication offerings have been slow to adapt to handling any real QoS concerns solely by the functionality contained within the replication and array areas. The task of collecting the metrics and then performing automated functions based on those metrics would be very slow and painful, based on the number of areas you would need to go to gather information (servers, storage, SAN, IP network, WAN and so on). This makes traditional replication implementations that have to meet a certain performance or utilization requirement very risky for resellers to guarantee.

The benefits of interconnect pathways

Using simple networking technologies to provide the interconnect pathways between the target and remote systems allows for even more flexibility in the replication solution. With thin replication, there's no need for complex FCIP engines on both sections of the replication segments. The deployment is as simple as plugging into the iSCSI connection on the storage system and then into your customer's network; then it's a matter of using already available pathways to gain access to the target systems. While FCIP is supported even by thin replication solutions, generally most customers default to iSCSI as the transport of choice since it's cheap and easy to use.

In more legacy-like deployments, not only would you need to purchase the FCIP engine, you'd also need to integrate it into your Ethernet and Fibre Channel networks. Typically, for a robust and redundant deployment, these devices are doubled to ensure physical-layer high availability in the replication link. The FCIP devices are fairly complex to configure and maintain over time.

Thin replication improves validation

Thin replication also enables storage administrators to test and verify that the disaster recovery and business continuity sites are in solid working order without affecting the production volumes at the source location. This allows a customer to perform a simple procedure to determine that the recovery time objective (RTO) and recovery point objective (RPO) can be met with no impact to the primary facility. These verification processes could be added to the daily, weekly or monthly checks to determine data integrity at the remote location, delivering a simulated disaster recovery process.

In a traditional replication environment, this functionality is almost nonexistent. Testing DR plans in real time requires a significant time investment from a number of IT groups within your customer's organization -- or the purchase of specific aftermarket products that provide that functionality.

With thin replication, no matter what topology the customer selects, the replication process can be configured, managed and monitored from one management console, minimizing the number of full-time employees needed to maintain and manage the system.

Disaster recovery is no longer a someday project; most medium-sized businesses require some form of near-real-time data replication. The good news is that the benefits of technologies like thin replication have significantly lessened both the cost of entry and the technical learning curve. The advanced features and functionality built into thin replication provide you and your customers with a flexible, simple and cost-effective replication solution to meet many enterprise needs.

About the author

George Crump is president and founder of Storage Switzerland, an IT analyst firm focused on the storage and virtualization segments. With 25 years of experience designing storage solutions for data centers across the United States, he has seen the birth of such technologies as RAID, NAS and SAN. Prior to founding Storage Switzerland, George was chief technology officer at one of the nation's largest storage integrators, where he was in charge of technology testing, integration and product selection. Find Storage Switzerland's disclosure statement here.


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