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Deduplication: When, Where and How

Deduplication gives you the ability to do more with less

Nearly every enterprise can benefit from deduplication. Business data has been growing exponentially. Routine backups of that data have become too costly or simply ineffective. Deduplication can help by reducing the cost of primary and secondary storage. Essentially, limited resources are made much more effective and efficient.

What most organizations don't realize is how much deduplication technology has matured. Originally, deduplication was used as an alternative to tape for backup and disaster recovery. This user case continues today and has become one of the predominant solutions for data protection. As it has matured, it has begun to evolve from being a point solution at the end of a backup chain (the target) to a player in every step of the backup process: at the client side, at the network side, at the media server side, as well as at the target device. Backup and storage vendors are implementing this technology in all aspects of their solutions.

Storage vendors have also recognized the efficiencies available by deduping data. In addition to implementing space efficiency technologies in their storage arrays, they're offering deduplication as a way to both improve available capacity and optimize data transmission when replicating data.

Versatile Technology
With these advancements it's possible to leverage deduplication to solve a variety of storage problems. In the data protection space, IT departments face increasing pressure to offer faster backups, even faster restores, and to do them with fewer resources than in the past. Data protection solutions that offer deduplication can, at the very least, significantly reduce the cost of protection to disk - often by more than a 20x reduction.

However, and perhaps more important, recovering lost information from these solutions is typically a lot faster than legacy tape solutions. A properly designed data protection solution that leverages deduplication can often either completely eliminate tape, or relegate tape to an archival medium. In addition, many companies using such a solution are able to replicate all of their backup data from one site to another. This eliminates the need for third-party tape handling and greatly improves the recoverability of the enterprise's data.

For enterprises that employ a replication strategy, deduplication can offer significant efficiencies depending on the data being replicated. If the data has a great deal of repetition or commonality, dedupe can offer tremendous boosts in performance. However, if the data is not very repetitious, deduplication will not offer as great an improvement. For most replication types, enterprises can expect a 2x to 4x reduction in bandwidth requirements.

More and more, storage vendors are offering deduplication on primary storage. Primary storage dedupe is a good idea when the data that is being stored has a lot of commonality - in other words, similar data being stored in one location. A good example of this is virtual environments. In such a situation, virtual machines are being stored as big files. Each has a lot in common - the operating system, unused blank space and, in many case, the applications themselves. Disk devices that can do primary storage deduplication would be able to reduce all of this data to a single instance. Regardless of the hypervisor used - VMware, HyperV and so on - there is a huge amount of commonality between each of the virtual machine instances. In fact, it's common to be able to reduce storage requirements in virtual environments by over 80% through deduplication.

Other primary environments, however, don't present a lot of common data, and thus will not benefit from deduplication. What's more, the process of uncovering which blocks of data have been seen before is expensive in both compute resources and I/O bandwidth. Both of those are at a premium in storage array controllers. A knowledgeable designer will typically look at the application type, the data type, and the resources available on the storage array that's doing the dedupe. Once all of these variables are factored together, it's possible to decide if it makes sense to use deduplication on primary storage.

Technique Pros and Cons
While there's a lot to consider when designing a deduplication strategy, a lot of the decisions are fairly nuanced. For example, the two most common techniques for performing deduplication are hashing and delta differencing. Backup appliances use one or the other, or in some instances a hybrid of the two. Which is the preferred technique depends on who you're talking to.

At a high level, hashing and delta differencing are very similar. The net effect of both is that common patterns of data are reduced and you end up with a greatly reduced storage requirement. The difference is in how you determine if there is a common pattern of data. With hashing implementations, the vendors run small blocks of the data through a mathematical algorithm and compute whether they have seen the same data before. This computation theoretically does not offer 100% certainty whether or not a piece of data has been seen before. However, statistically it is almost a certainty - so much so that you'd be more likely to win the mega lottery - dozens of times in a row. The consensus is that this is good enough, and most vendors have used hashing to develop their solutions.

For reasons involving technical implementation, performance tradeoffs, and arguably higher reliability, some vendors have chosen to develop their solutions through delta differencing. With this technology, each small piece of data is actually compared, bit for bit, with everything that has been seen before. This guarantees that the data has or has not already been seen.

Regardless of the implementation used, the odds are more in favor of external failures s power outage, water damage, satellite falling on the data center - than on technologies that determine how data bits are identified as the same. In most deduplication designs it's more important to focus on the features and functionality of the overall solution, rather than this specific level of detail.

Another topic has to do with the timing of deduplication. Inline deduplication processes dedupe backup data in real-time, as it's received at the front end of the Virtual Tape Library (VTL) or Disk-to-Disk (D2D) device. Post-process methods, on the other hand, remove duplicate data after the backup has completed. Regardless of which method is used, the same amount of work is being done.

The question of whether it makes more sense to do inline or post-process deduplication can best be answered by, "it depends." Regardless of when you do it, deduplication is inherently an expensive thing to do in terms of CPU and I/O resources. Choosing between inline and post-process is essentially choosing between paying for the service upfront or after. With some vendors' technologies, you have no choice. You have to use either inline or post. With others you get the choice, although it's something of a black art to figure out when to best use one versus the other.

Typically it comes down to optimizing the speed of ingest (how fast you get the data into the device) with rehydration (how fast you get the data back), and striking a balance between the two. Your best recommendation is to work with someone who has earned the scar tissue from using both these technologies.

Achieving Maximum Efficiency
Now that deduplication is so prevalent, the challenge most of our customers face is identifying which one to use and when. This is particularly difficult since each vendor unequivocally states that their solution is better than everyone else's and is the "one true way." In reality, there are no simple black and white answers and each solution's merits must be weighed individually.

To develop the best possible deduplication solution, it's important to first determine the problem you're trying to solve. Conduct an internal analysis, and then approach a partner who has an unbiased approach to solving the issue at hand. The right partner can help you sort through the hype and identify solutions and best practices that will align with your business needs.

The benefits of deduplication are many. Capital expenses are greatly reduced; you need fewer disks, less tape, and less bandwidth to accomplish the same task. If used appropriately, deduplication will also improve your operational efficiencies, which you can then leverage to reduce your operational expenses.

Simply put, deduplication gives you the ability to do more with less. Whether in networking, primary storage, backup or for data archival protection, a well-designed deduplication solution can help you mitigate the challenges of big data - and keep your IT landscape lean, fast and efficient.

More Stories By Juan Orlandini

A practice manager for Datalink, Juan Orlandini is a 25+ year veteran of the open systems IT industry. Throughout his career, he has been involved in the design and deployment of many large and advanced storage, data protection, and high availability infrastructures.

Juan evaluates next-generation technologies for Datalink and also works with end users, assisting them with architecting and implementing strategic data center architectures. In his current role, he is developing managed services offerings designed to help companies optimize staff productivity and data center efficiency. He continues to evaluate industry solutions, customer needs, and blogs about it at blog.datalink.com

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