A Complete List of VMware VAAI Primitives

Good post from Stephen Foskett (thank you) around the VMware VAAI Primitives

VMware’s introduced the “vStorage APIs for Array Integration” (VAAI) in vSphere 4.1, and block-heads like me went nuts. We’ve been trying to integrate storage and servers for decades, and VMware’s APIs finally allowed this to work in truly seamless fashion. But the world of VAAI is a thicket of bizarre naming and puzzling functionality. Some VAAI primitives are ignored or even hidden! Let’s take a look at the complete list.

VAAI in 4.1: Three For Block (Plus One More)

vSphere 4.1 officially includes three VAAI primitives: Full Copy, Hardware Assisted Locking, and Block Zeroing. But it was intended to include a fourth (Thin Provisioning Stun) and variations in nomenclature have confused administrators.

Here’s the complete list of VAAI primitives in vSphere 4.1, including a little more about what they really do.

Official Name


What does it do?



Atomic Test & Set (ATS) Hardware Assisted Locking Enables granular locking of block storage devices, accelerating performance Y N/A
Cloning Blocks Full Copy, Extended Copy Commands the array to make a mirror of a LUN (Clone, VMotion) Y N
Zeroing File Blocks Block Zeroing Communication mechanism for thin provisioning arrays Y N/A
Out of Space Condition Thin Provisioning Stun “Pause” a running VM when capacity is exhausted Y Y*

A complete list of VAAI primitives in vSphere 4.1

*Note: Thin Provisioning Stun is officially a vSphere 5 VAAI primitive. It was included in vSphere 4.1 and some array plugins support it, but it was never officially listed as a vSphere 4 primitive

Read on here

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