Thin Provisioning

Thin provisioning is the act of using virtualization technology to give the appearance of having more physical resources than are actually available. If a system always has enough resource to simultaneously support all of the virtualized resources, then it is not thin provisioned. The term thin provisioning is applied to disk later in this article, but could refer to an allocation scheme for any resource. For example, real memory in a computer is typically thin provisioned to running tasks with some form of address translation technology doing the virtualization. Each task believes that it has real memory allocated. The sum of the allocated virtual memory assigned to tasks is typically greater than the total of real memory.

The efficiency of thin or thick/fat provisioning is a function of the use case, not the technology. Thick provisioning is typically more efficient when the amount of resource used is very close to the amount of resource allocated. Thin provisioning is more efficient where the amount of resource used is much smaller than allocated so that the benefit of providing only the resource needed exceeds the cost of the virtualization technology used.

Just in time allocation is not the same as thin provisioning. Most file systems back files just in time but are not thin provisioned. Overallocation is not the same as thin provisioning; resources can be overallocated / oversubscribed without using virtualization technology, for example overselling seats on a flight without allocating actual seats at time of sale, avoiding having each consumer having a claim on a specific seat number.

Thin provisioning is a mechanism that applies to large-scale centralized computer disk storage systems, SANs, and storage virtualization systems. Thin provisioning allows space to be easily allocated to servers, on a just-enough and just-in-time basis.