Like Facebook for employee use and iPhones in business, data storage policy is a topic that can be a political hot potato within corporate walls.

Implementing policy-based storage management can be so contentious, in fact, that at many companies, it quickly turns into a non-starter. Rather than haggling with the business about where data gets stored and for how long, IT simply places all data in a single tier - that which is most satisfactory for the most critical applications. The result is the stereotypical high-cost, over-provisioned storage-area network.

Andrew Reichman, an analyst at Forrester Research, calls this the "highest common denominator" approach to policy-based storage management.

"Companies really struggle with how to do policy-based storage management right, so in some cases they do nothing. They just don't tier at all," he says.

"Everybody's application is performance-sensitive and important, or you wouldn't be deploying or supporting it. What's needed is the relativity -- how much performance capability is truly needed for this important application to work effectively?" Reichman adds.

"The challenge isn't with the cost of the hardware or the software or in the tools for moving the data," agrees Greg Schulz, an analyst at The Server and StorageIO Group. "It's in getting somebody to define and sign off on what to move, when to move it, how long to keep it, how many copies to keep, when to delete it, and how to handle the deletion. This takes someone who has a business-value understanding of the applications and who can interface with technologists to bring all this together, and who also can get approval from the business that this is what can be done, this is what needs to be done, and also, by the way, will indemnify it."

And when dealing with data files, storage policies are only as good as the level of user compliance, adds Kerry Sylvester, IT director at WaterFurnace International, a manufacturer of heat pumps.

At the Fort Wayne, Ind., company, Sylvester uses FalconStor Software's virtualisation technology to move data across its storage tiers, but users don't always store the data as directed, he says. "Some people like to hang on to stuff, and habits are hard to break. To make policy-based storage work, you need your users storing their documents to the right places," says Sylvester.

If politics and culture aren't distracting enough, a lack of knowledge often stands in the way of good policy-based storage management, Reichman adds.

"Performance analytics in storage is pretty binary and often trial-and-error-based," he explains. "So there's often no way to make a confident decision and say, 'This will perform completely effectively on a lower class of performance system.' So a lot of it is guesswork - and that means there'll be mistakes sometimes, and as a result IT alienates the user community."

But the politics of storage are starting to change with advanced automated data tiering. Available from companies like 3Par (which has agreed to be acquired by Hewlett-Packard), Compellent Technologies and EMC, this technology monitors how data is being used at the block level, determines which data should be on which type of storage, and then moves it there.