When we allocate disks in VMware, we have to specify thin provisioned, thick provisioned eager zero or thick provisioned lazy zero, but what is the difference?
This is taken from the documentation:
Thick Provision Lazy Zeroed
Creates a virtual disk in a default thick format. Space required for the virtual disk is allocated when the virtual disk is created. Data remaining on the physical device is not erased during creation, but is zeroed out on demand at a later time on first write from the virtual machine.
Using the default flat virtual disk format does not zero out or eliminate the possibility of recovering deleted files or restoring old data that might be present on this allocated space. You cannot convert a flat disk to a thin disk.
A type of thick virtual disk that supports clustering features such as Fault Tolerance. Space required for the virtual disk is allocated at creation time. In contrast to the flat format, the data remaining on the physical device is zeroed out when the virtual disk is created. It might take much longer to create disks in this format than to create other types of disks.
Use this format to save storage space. For the thin disk, you provision as much datastore space as the disk would require based on the value that you enter for the disk size. However, the thin disk starts small and at first, uses only as much datastore space as the disk needs for its initial operations.
Hi - I guess by now you understand the basic definitions of these different Virtual Disk Provisioning Policies through articles like vSphere Documentation Center
However, would suggest you to check this Eager thick vs Lazy thick disk performance | Rickard Nobel to understand these disk provisioning policies in detail that would probably help you more.
you would provision eager zero'd when you need fast write performance. perhaps for a DB or an Exchange DAG. personally I have not used them all that much as the time laying them out is quite long and it is very intensive on your Shared storage.
Thin provision: is when the disk is created but the size of the disk is equal to the size of the content. Lower write performance.
Thick provision lazy zeroed: the disk created has the same size as the storage on the storage, but the blocks inside are initialized immediately before being written. Average performance.
Thick provision eager zeroed: the disk has the same dimensions as the ones that are set but the blocks inside are cleared at the time of creation, so the performance will be better.