1. A method for issuing a command to deallocate free storage blocks previously allocated to a logical block device, comprising: identifying a set of free blocks to be released from a data structure maintained by a hypervisor of a virtualized computer system; allocating the free blocks in the set to a file and marking the free blocks allocated to the file as used in the data structure; and issuing a command to the logical block device to deallocate the free blocks allocated to the file.