Implementing a Tiered Storage Strategy

The cost of storage continues to decline even as the capacity of individual drives increases. But rather than move all data to the fastest -- and most expensive -- devices, most enterprises are implementing a tiered storage strategy, in which data is delegated to devices according to its importance.

"Ten years ago, people simply installed systems that allowed them to store all information electronically and to get to it quickly," says Joe Martins, a partner with the Data Mobility Group LLC, in Nashua, N.H. "They didn't start to consider strategies that took into account cost as well as performance issues until 2000," when resolving Y2K issues brought it to their attention.

Dividing the Data
The Enterprise Strategy Group estimates that about 85 percent of the data sitting on high-end storage systems is non- or post-transactional, and that half of this replicates non-transactional data. "This is a very inefficient use of high-end real estate at best -- and a costly business adventure at worst," says Heidi Biggar, an analyst with the Enterprise Strategy Group, based in Milford, Mass. After all, primary disk storage is expensive to acquire, manage and maintain, as well as draining power and cooling resources.

Best practices involve first classifying data into categories. Information deemed mission-critical and data that is frequently accessed and/or changed should be (article continues)


kept on primary storage systems. Data that is less urgent but still important to the business could be kept on SATA-based systems. Data that is static, or only periodically accessed, could be kept on disk-based archives. Finally, tape or optical storage would be used for deep archiving.

Five Storage Strategies
How can you effectively implement a tiered storage system? Here's a five-step plan:

Determine your goals What do you hope to achieve from moving to tiered storage? Reduce costs? Improve performance? Achieve better service levels? Some combination of the above? "Some enterprises are extremely cost-sensitive and are looking to cut storage-related expenses," says Greg Schulz, founder of the StorageIO Group, in Stillwater, Minn. "Others put performance first, as it can directly impact their ability to serve customers. Before you do anything, you have to establish your priorities."

Establish recovery point objectives and recovery time objectives for all data types Before you can determine what data belongs on what kind of storage device, you must decide your recovery point objectives (RPO) -- the point in time to which data must be restored to ensure smooth recovery of business processes that the data supports -- as well as your recovery time objectives (RTO), the maximum amount of time that you can afford for systems to be down after a failure. Without both an RPO and an RTO, you will not be able to implement a viable storage tier strategy. It's not good enough to define one or the other; you have to specify both. (article continues)


Inventory existing storage resources Chances are good that you already possess a number of the storage devices you need to implement a tiered strategy with a minimal investment in additional equipment and software. Find out exactly what you already have installed that can be repurposed into a tiered strategy.

Consider how to best manage the increased complexity Moving to a tiered system always adds complexity to data center operations, but especially so if you switch from a single vendor to a multiple vendor storage environment. "Make sure you have the software tools, as well as the personnel to manage this cost-effectively," says Mike Karp, a senior analyst and head of the storage practice at the Enterprise Management Associates, in Boulder, Colo. "You don't want to gain efficiency in one area only to lose it in another."

Approach the process in phases Rather than implementing it all at once, it's best to start with one application and two data tiers, and proceed gradually from there. "This makes the process much more manageable -- and there are still immediate and sizable benefits," says Biggar.

All experts agree: Don't write that P.O. for the new drive until you complete your upfront work. "There's so much more involved than simply deciding what product to buy," says Karp.

Establishing a tiered storage system involves a lot of upfront work and investment in both time and hardware and software. There's no magic bullet for making it a success, warns Martins. But, he quickly adds, "It pays off in spades in the long run."