1. A method for storage virtualization comprising: providing a storage virtualization system connected to a network-attached storage (NAS) system, the storage virtualization system being separate and apart from the NAS system, the NAS system storing a plurality of data objects, the storage virtualization system having a primary memory store and a secondary memory store, wherein the primary memory store and the secondary memory store are non-volatile memory systems; storing, in the primary memory store, a first data structure containing first metadata for at least one of the plurality of data objects stored in the NAS system, and a second data structure containing second metadata for the at least one of the plurality of data objects stored in the NAS system, the second data structure having a larger memory footprint than the first data structure, the first metadata directing the storage virtualization system to the second data structure to obtain corresponding second metadata for the at least one of the plurality of data objects; identifying a least recently used data object of the plurality of data objects stored in the NAS system, the least recently used data object having corresponding second metadata in a corresponding second data structure stored in the primary memory store; and storing, in the secondary memory store, a third data structure containing the corresponding second metadata for the least recently used data object, the first metadata being modified to direct the storage virtualization system to the third data structure to obtain the corresponding second metadata.