dd命令错误输出的大小超过VMWARE中的分配大小

There is a VM on MAC os which is allocated 100G HDD. When i use dd command to shrink its size by populating the whole disk with 0, it errors out(no empty space left) when the size is increased to 120G instead of 100G. Why it throws the "no space left" exception with 120G but not the allocated 100G?There is a VM on MAC os which is allocated 100G