Primer: Thin Provisioning
What is it?
Thin provisioning is a relatively new way of assigning the physical disk capacity of a network storage system to logical volumes and specific applications. The goal is more efficient and cost-effective use of storage.
Why consider it?
Conventional storage management methods can result in large amounts of storage capacity sitting idle because of overly generous provisioning. Database and storage administrators tend to allocate too much space rather than too little. So, unused disk space winds up being inaccessible to other applications that could use it.
How does it work?
Thin provisioning takes some of the guesswork out of provisioning storage for a given application. Administrators can still estimate how much storage to reserve, but the partitions between logical storage volumes aren't as rigid as in conventional systems. Volumes can be assigned a maximum capacity but only consume as much disk space as they actually use, expanding as needed across a pool of multiple disks.
When systems monitoring tools show that free storage space is dipping too low, customers simply buy more capacity, according to David Scott, CEO of 3PARdata, a storage area network vendor that supports thin provisioning. With traditional provisioning, he says: "It costs you money to keep unused disks spinning in your data center, costs you more money to cool them down, and it costs you floor space."
According to company literature, a 4.6-terabyte 3PAR system priced at $138,000 can fill the same need as a traditionally provisioned system that would require 18 terabytes of disk space and cost $540,000.
"We're hitting 80% to 85% utilization for our storage, whereas before we were at maybe 50% because you had to have a lot in reserve," says Jess Carruthers, a project manager at William Beaumont Hospital in Troy, Mich., who has used Network Appliance's thin provisioning to support the company's Oracle applications.
How significant is it?
At Gartner's Symposium conference in October, analyst Roger W. Cox listed thin provisioning as one of the five key developments impacting storage, even though it has not yet been embraced by the largest vendors. "There's only one name brand in thin provisioning, and that's Network Appliance," he said. That may change, however, as thin provisioning turns up in new products from EMC, IBM and others.
Tony Asaro, senior storage systems analyst with Enterprise Strategy Group in Milford, Mass., says he can find no evidence that thin provisioning hurts performance or increases the risk of exceeding physical storage capacity. After interviewing representatives of 30 companies using thin provisioning setups, he found that 67% reported no technical problems, and 70% would rank thin provisioning high on the list of their requirements for future systems.
When does it make sense?
Asaro acknowledges that thin provisioning isn't for everyone. "You don't need thin provisioning when you know how much storage you need today, there isn't a great deal of growth, or the growth is predictable and infrequent," he says.
Most thin provisioning users have storage requirements that grow at unpredictable rates. MySpace.com adopted 3PAR storage to support its member databases primarily because of the equipment's high input-out capacity, but also because by delaying the purchase of new storage until it's needed, the system helps contain capital expenditures.