Question: 20
Under which two conditions can vStorage APIs for Array Integration (VAAI) provide a performance benefit? (Choose two.)
A. When a virtual disk has VMDK files stored on an NFS datastore.
B. When a virtual disk is created using the New Virtual Machine wizard.
C. When cloning a virtual machine with snapshots.
D. When a virtual disk is deleted.
Answer: AD
Explanation:
A) With NFS, the default is alway thin provisioned. Provisioning there should not have much benefit from VAAI offloads, except when you are not creating a thin disk. In that case, you utilize the "space reservation" function of VAAI, which allows you to create an EZT disk, but that doesn't really mean I am creating the disk a lot faster. Actually, I'm not offloading the writing of zeroes at all via NFS, so performance is not the key part of this VAAI function.
B) The answer doesn't tell met what option is selected, regardless of the option I choose, I can either use features like for example ATS or Write-Same, depending on which type of disk I'm provisioning (obviously this applies to block storage).
C) VMware KB 1021976 clearly states "VAAI hardware offload cannot be used when: [..] Cloning a virtual machine that has snapshots (or doing a View replica or recompose), because this process involves consolidating the snapshots into the virtual disks of the target virtual machine". So this answer isn't correct in my opinion.
D) You should distinguish between the deletion of an entire disk, and the space reclaim function for thin provisioning (TP Unmap) which is covered by Cormac here: The Unmap primitive was actually introduced with vSphere 5.0, and did include the feature that, when a VM was vMotioned to a different disk, or a VM was deleted, Unmap would reclaim the space. Unfortunately, they noticed that this could cause a performance problem, and they disabled the primitive the vSphere 5.0 patch 2. They then re-enabled it, but as a manual process with vSphere 5.0U1.
