1. A method for performing lock free processing of metadata for storage devices in a virtualization system, comprising: identifying metadata for the virtualization system, wherein the metadata comprises a first map corresponding to virtual disks, a second map corresponding to extent identifiers, and a third map corresponding to groups of extents; using a processor to perform lock-free access of the metadata in a first order comprising first accessing the first map, then accessing the second map, followed by accessing the third map; and performing lock-free modification of the metadata in a second order comprising first accessing the third map, then accessing the second map, followed by accessing the first map.