The vStorage API for Array Integration (VAAI) is a new API for storage partners to leverage as a means to speed up certain functions that, when delegated to the storage array, can greatly enhance performance. This API is currently supported by several storage partners and requires these partners to release a special version of their firmware to work with this API. In the vSphere 4.1 release, this array offload capability supports three primitives:
- Full copy enables the storage arrays to make full copies of data within the array without having the ESX server read and write the data.
- Block zeroing enables storage arrays to zero out a large number of blocks to speed up provisioning of virtual machines.
- Hardware-assisted locking provides an alternative means to protect the metadata
http://www.vmware.com/files/pdf/techpaper/VMW-Whats-New-vSphere41-Storage.pdf
