In vSphere 4 the VAAI test harness only included functionality.  So if a storage array supported the VAAI primitives and passed VMware’s functionality test then VAAI was listed as a feature of the supported array in the Storage/SAN Compatibility Guide.  vSphere 5 added a VAAI performance test.  This is due to some of the issues it discovered when it released their Thin Provision Reclaim VAAI feature in vSphere 5.

EMC’s CX4 did not pass VMware’s performance test harness for XCOPY/Block Zero.  Atomic Test and Set (ATS) Hardware Offloading did pass the performance testing but since the XCOPY/Block Zero didn’t pass then VMware considers all VAAI as unsupported on the CX4.

Chad Sakac (Virtual Geek) lays it all out at the end of the PPT and recording in the post VNX engineering update, and CX4/VAAI vSphere scoop.  In that he proposes the following EMC support model:

  • Running with VAAI block acceleration on a CX4 with ESX5 is considered an unsupported configuration by VMware.
  • EMC will support the use of VAAI block under ESX5 with CX4 arrays.
  • If customers running this configuration have an issue, EMC recommends they turn off the VAAI features. If the condition persists, VMware will accept the case. If the problem is no longer occurring, contact EMC for support.

vSphere 4 did not have a performance test harness.  So if they were happily running vSphere 4 with VAAI enabled then they can upgrade to vSphere 5, leave VAAI enabled, and likely enjoy the same experience they have now for their CX4 on vSphere 4.