With the release of vSphere 4.1, we finally get to see the first revision of the vStorage API for Array Integration (VAAI) features. This initial release provides the following SCSI driver primitives with VAAI supported storage arrays:

  • Write Same/Zero - Eliminating redundant and repetitive write commands, tells array to repeat via SCSI commands.
  • Full Fast/Copy - Leverage array to mass copy, snapshot and move blocks via SCSI commands.
  • Atomic Set and Test - Stop locking LUNs and start locking blocks.
  • Thin Provisioning Stun - Reporting array TP state to ESX.

The above definitions were taken off of an EMC presentation found here. VMware has also published a new VMware KB article regarding VAAI FAQ, take a look here at KB1021976.

Though these features are not specific to any one storage array vendor, the vendors themselves are required to implement these primitives within their array OS software for them to be available. If all prerequisites are met, and you have an ESX or ESXi host running on vSphere 4.1 and VAAI supported storage array, these new storage operations will now offload to the array versus running within the VMkernel.

However, if you do not have an array that supports VAAI, the new version of ESX and ESXi will still try to use these features. As I understand from an earlier discussion of VAAI, there is one additional operation that is performed and it's impact is supposed to be insignificant (please correct me if I'm wrong). Though if you would like to disable these VAAI features or would like to see the difference between a non-VAAI and VAAI operation, it is controlled with the following three advanced host configurations.

VMFS3.HardwareAcceleratedLocking - Atomic Test and Set
DataMover.HardwareAcceleratedMove - Full/Fast Copy
DataMover.HardwareAcceleratedInit - Write Same

By default, all three of these configurations are enabled with a default installation of vSphere 4.1. The following vSphere SDK for Perl script allows a user to enable or disable VAAI configuration on a set of hosts defined in an input file. The script allows you to connect to vCenter if your hosts are being managed by vCenter or directly to a specific ESX or ESXi host and provide the following parameters:

--hostlist = Lists of ESX(i) hosts to perform operation _IF_ they're being managed by vCenter (default is ALL hosts in vCenter)

--operation = Operation to perform (query|enable|disable)

Download: vaaiHWAccelerationMgmt.pl

Here is an example of the host input file:

[[email protected] scripts]$ cat hosts

Here is an example of querying for VAAI configurations:

Here is an example of disabling VAAI configurations:

Here is an example of disabling VAAI configurations:

For more information about vStorage APIs, take a look here.

Thanks for the comment!