1. A method for performing lock free processing of metadata for storage devices in a virtualization system, comprising: identifying a metadata structure hierarchy with a plurality of levels including at least a first level corresponding to a virtual storage unit and a mapping between portions of the virtual storage unit to contiguous physical storage, and a second level corresponding to information describing the physical storage; reading from the metadata structure in a first order from the first level to the second level without locking; and writing to the metadata structure in a second order from the second level to the first level without locking, wherein the second order is opposite of the first order.