what is allocation information means

[baber]

Dear all

Hi

in vsphere documents write there s a new feature in VR-6 that work just on esxi 6.0 and 6.5  with name The acceleration of initial synchronization and it say this just work  for vms with 

Lazy zeroed thick disks, thin disks, and vSAN sparse disks, Space-Efficient

sparse disks

and eager zero thick disks don't provide allocation information and this means if my vms have thick provision eager zero  acceleration of initial synchronization will not work  now i want to know what is means allocation information ?

can you say an example plz ?

BR