Thin provisioning, pioneered by small vendors such as 3PAR (now part of Hewlett-Packard Co.) and Compellent Technologies (which Dell Inc. plans to acquire) that have been acquired by larger companies, is a method of allocating storage to servers on a just-enough and just-in-time basis.
According to the TheInfoPro's most recent 2010 end-user survey, approximately 51% of Fortune 1000 and midsized enterprise IT organizations use thin provisioning, with 25% piloting or planning to implement thin provisioning. Fewer than 25% say they don't plan to use it. Thin provisioning ranks as the number two technology behind Information Lifecycle Management (ILM) on the analyst firm's Heat Index, said Marco Coulter, TheInfoPro's managing director of storage.
"According to our Heat Index, a number of people are still exploring the technology, but this is where the profession is going," Coulter said.
As hot as thin provisioning is, Gestalt IT consultant Steve Foskett warns it's still not for everyone. Foskett admits there have been improvements to the technology in recent years around reclamation but said de-allocating storage can still be a problem.
"Hosts have no concept of thin provisioning," he said. "All they know is, 'This is my storage.' That's all the hosts have been able to know. People are tempted to use thin provisioning to overallocate storage. And once you have written data to disk, it's difficult to reclaim it. I'm not a fan of a capability that's not effective. If there's a way to allocate and not a way to de-allocate, then it's not effective. I'm concerned people would use it as a band aid for a business problem. People are tempted to use thin provisioning to overallocate storage. Once you've written data to a disk, it's difficult to reclaim it."
Symantec Corp., working with 3PAR and other vendors, in recent years has made improvements in the thin reclamation process. Dan Lamorena, director in Symantec's Storage and High Availability Group, said the software vendor can reclaim storage blocks not being used and put them back in the storage pool.
"We have thin reclamation because we have visibility into our file system," he said. "Reclamation is an issue, but it's not the issue. People worry they haven't provisioned enough storage. They honestly don't know how much storage is being consumed. They don't know how much the application is using."
HP's 3PAR, Compellent, EMC Corp., Hitachi Data Systems, IBM, NetApp and others support Symantec's Thin Reclamation API in their arrays. 3PAR also has what it calls an ASIC-based zero detection mechanism that essentially reclaims unused disk capacity. 3PAR made a thin conversion feature available in Sept. 2009 that makes fat volumes thin when migrated off a legacy array.
Administrators using thin provisioning say they take steps to make sure it remains effective over time. They often carefully track their storage usage, monitoring how much storage they have used over a period of a year or more. They project how much their storage will grow in the coming years, and give their systems a certain percentage of overallocated storage as a buffer to make sure they're not going to be caught underprovisioning.
Brandon Jackson, CIO of Gaston County in North Carolina, has used thin provisioning for five years now on his Compellent Technologies Storage Center system. He said he turned to thin provisioning when he first implemented a SAN because he knew Gaston County's storage needs would grow significantly but he didn't know by how much. Gaston County has two 70 TB Storage Center SANs.
"Thin provisioning allows you to buy storage slowly, so you don't have to risk buying too much," he said. "You can do reclamation with Compellent but the real question is, do you really need to reclaim it?"
Jackson said his organization monitors storage allocation during a two-and-a-half-year period, and projects how much storage will grow with a plus or minus 10% accuracy of overallocation as a buffer. Thin provisioning, he said, has eliminated a major administrative nightmare. "Our system administrators were spending a lot of time moving applications to different servers, talking to end users about what to archive and what to delete or what servers to buy disks for. All those administrative headaches are gone," he said.
Chris Carlton, storage team leader at Health Technology Solutions at JPS Health Networks in Fort Worth, Texas, said he implemented thin provisioning on his Hitachi Data Systems Universal Storage Platform (USP) array last year. He said one of the benefits of the technology is that you can "spread the disk space across a greater number of spindles." Still, he said, "there's always a concern. You don't have control over the end user, so if the system is overloaded you'll have a problem. But we know our growth and how much it's going to grow every year. We try to keep the pool overprovisioned by 20%. It's our buffer that we set and monitor. We're currently comfortable with that."
Michael Passe, IT storage architect at Beth Israel Deaconess Medical Center in Boston, said he started thin provisioning his EMC Clariion array last summer for test and development servers, which comes to approximately 10% to 15% of the medical center's total servers. He said all future arrays he buys will use thin provisioning across the board.
Passe said he also adds space as a buffer. He uses a 2-to-1 ratio. "I think there's some fear surrounding the technology as to what applications play well with it and which won't," he said "We double it, then we depend on our system administrators to monitor the allocation. [The storage] is just used as it's needed."
One of the most important aspects, Passe said, is that communication between storage and server administrators flows both ways to ensure the technology is being used properly. "As long as everyone is working in unison and understands the technology, and as long as everybody talks to each other, it can be a win,' he said. "If they don't, there could be issues."
Passe predicted that as the technology evolves, "you will see everybody going this way. You will see the traditional way of doing storage go away… fat LUNs will go away."