VAAI – vStorage APIs for Array Integration (VAAI) is a set of features that enables a VMWare ESXi host to offload virtual machine (VM) and storage management operations to a storage array. VAAI is a set of storage array operations aimed at reducing host CPU load and storage network bandwidth. VAAI consists of three components that VMware refers to as primitives. A primitive is the underlying technology that a higher-level feature or use case can call. In turn, the primitive can perform a function or request that the function be performed on the storage device on behalf of the primitive. These primitives are as follows:
- Atomic Test & Set (ATS), which is used during creation and locking of files on the VMFS volume
- Clone Blocks/Full Copy/XCOPY, which is used to copy or migrate data within the same physical array
- Zero Blocks/Write Same, which is used to zero-out disk regions
- Thin Provisioning in ESXi 5.x and later hosts, which allows the ESXi host to tell the array when the space previously occupied by a virtual machine (whether it is deleted or migrated to another datastore) can be reclaimed on thin provisioned LUNs.
- Block Delete in ESXi 5.x and later hosts, which allows for space to be reclaimed using the SCSI UNMAP feature.
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