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Virtual provisioning is a strategy for efficiently managing space in a storage area network (SAN) by allocating physical storage on an "as needed" basis. This strategy is also called thin provisioning.
Virtual provisioning is designed to simplify storage administration by allowing storage administrators to meet requests for capacity on-demand. Virtual provisioning gives a host, application or file system the illusion that it has more storage than is physically provided. Physical storage is allocated only when the data is written, rather than when the application is initially configured.
Virtual provisioning can reduce power and cooling costs by cutting down on the amount of idle storage devices in the array. As a result, virtual provisioning has become a part of green computing and green data center initiatives. The caveat for virtual provisioning is that it requires administrators to carefully monitor the usage of virtually provisioned resources to ensure that no virtual disks become full, resulting in storage errors for mission-critical applications.