VAAI NAS introduced the ability to create LazyZeroedThick & EagerZeroedThick disks on NFS datastores. Without VAAI NAS, one can only create thin VMDKs on NFS datastores. For those of you who are using VAAI NAS plugins, there is an important note in the 5.0U1 release notes that you should be aware of.
ESXi cannot distinguish between thick provision lazy zeroed and thick provision eager zeroed virtual disks on NFS datastores with Hardware Acceleration support
When you use NFS datastores that support Hardware Acceleration, the vSphere Client allows you to create virtual disks in Thick Provision Lazy Zeroed (zeroedthick) or Thick Provision Eager Zeroed (eagerzeroedthick) format. However, when you check the disk type on the Virtual Machine Properties dialog box, the Disk Provisioning section always shows Thick Provision Eager Zeroed as the disk format no matter which format you selected during the disk creation. ESXi does not distinguish between lazy zeroed and eager zeroed virtual disks on NFS datastores.
This can be confusing, especially if you select “Thick Provision Lazy Zeroed” when creating a virtual machine disk during deployment, and later you edit the properties of the VM and it states that the disk is “Thick Provision Eager Zeroed”. This is the crux of the issue; we will always report Eager Zeroed, even if the VMDK is Lazy Zeroed. Some of the guys at EMC have already run into the issue, which I how I got a heads-up on it.
On VMFS, we can query TBZ (To Be Zeroed), which can tell us that there are blocks that are provisioned but not yet initialized. I wrote an KB article on how you can do this via vmkfstools. On NFS, we have no way of retrieving this information.
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