[ovirt-users] Understanding Preallocation (Actual) Size of a thin DIsk

HI , I need to know about the Pre allocation size of a thin disk while creating a disk in a storage domain . Can we change the actual size (allocated Size ) after disk creation .Can anyone can enlighten me on how it will increase when the size of the disk exceeds the allocated limit ? If I try to write to the disk from the hypervisor , the write gets failed after the allocated size whereas if i create a thick disk i am able to write till the disk capacity Regards Shafi