Continuous data protection (CDP), as defined by the Storage Networking Industry Association (SNIA), is a methodology that continuously captures or tracks data modifications and stores changes independent of the primary data, enabling recovery points from any point in the past. CDP systems may be block-, file- or application-based, and can provide fine granularities of restorable objects to infinitely variable recovery points.
That last bit -- infinitely variable recovery points -- is what separates true CDP from near-CDP. Near-CDP relies on periodic snapshots replicated to a secondary system. This allows users to roll back data to specific points in time, typically between 15 minutes to an hour, rather than any point in time. So, the recovery time objective (RTO) with near-CDP and true CDP are the same, almost instantaneous, because you have a secondary system ready to go. The recovery point objective (RPO) is equal to the frequency that snapshots are created and replicated.
Jason Buffington, senior analyst with Enterprise Strategy Group, said that is likely to be adequate for most organizations.
"SNIA says that CDP must be able to recover to any point along a timeline -- most people don't need that level of granularity. Fifteen minute intervals are likely to be good enough," he said. "I think that definition is flawed. Near-CDP reflects life in the real world. SNIA's definition is unnecessarily narrow and theoretical."
Greg Schulz of Storage and Server IO agreed. "Those [vendors] that tried to survive or create a market have been overtaken by those who provide CDP as a function," he said. "The whole focus on pure CDP, fine grain, coarse grain or near-CDP has fallen by the wayside and shifted to how different products' capabilities address different needs. Near- or coarse-CDP including frequent snapshots is good enough for most environments and applications."
One area where true CDP endures is among endpoint backup solutions. "Many of the leading endpoint backup tools today transmit changes as soon as they are written to the disk," said Rachel Dines of Cambridge, Mass.-based Forrester Research. "But even in this space, there is some confusion. Some solutions call themselves CDP, but actually monitor for changes on a periodic basis."
CDP is still under consideration by many companies, but interest is growing. According to the recent TechTarget Purchasing Intentions survey, 22% of respondents planned to increase CDP spending in 2013.
Buffington said many organizations could benefit from the technology. "It doesn't take a lot of user dependency on any given application to justify the use of near-CDP alongside backup," he said. "It can be accomplished at the file, block or application level, and all are appropriate and viable cost-wise or otherwise, given the environment."