1. A system to reclaim space identified as no longer in use, the system comprising: a virtual logic unit (vLUN) layer that corresponds to one of a plurality of layers in an input/output (I/O) path of a computer system, the vLUN providing a plurality of logical chunk addresses (LCAs) to layers disposed above it in the I/O path, such that the LCAs in the vLUN are the only LCAs visible to layers above the vLUN; a thinly provisioned mapped logical unit (mapped LUN) layer disposed below the vLUN in the I/O path and being in operable communication with the vLUN, the thinly provisioned mapped LUN being in operable communication with a pool of storage units that provide, as requested, storage to the thinly provisioned mapped LUN, the thinly provisioned mapped LUN having associated therewith a storage extent of a predetermined size, the storage extent defining a minimum size of storage that the thinly provisioned mapped LUN can be directed to allocate or deallocate from the pool, wherein the mapped LUN is associated with a plurality of physical chunk addresses (PCAs), each PCA configured to provide physical storage for a respective chunk of data; a mapping layer disposed between and in operable communication with the vLUN and the thinly provisioned mapped LUN layers, the mapping layer defining a layout of the thinly provisioned mapped LUN that helps improve the efficiency of input/output (I/O) access to the mapped LUN, the layout comprising: a first region comprising a set of first PCAs, each first PCA being allotted to provide physical storage for a respective first chunk of data stored at a single first corresponding LCA in the vLUN; a second region comprising a set of second PCAs, each second PCA being allotted to provide physical storage for a respective second chunk of data, where the second chunk of data corresponds to data that is associated with at least two LCAs; and a metadata region, the metadata region including a first portion indicating, for each LCA in the vLUN, whether the corresponding PCA for the LCA is in the first region or the second region of the mapped LUN, and a second portion providing, if the corresponding PCA is in the second region of the mapped LUN, mapping information for the LCA to the corresponding PCA in the second region, wherein the first portion of the metadata is stored in the memory of the computer system to help improve the efficiency of I/O access to the chunks of data stored in the mapped LUN; a data reduction engine in operable communication with the mapping layer, the data reduction configured to: perform a data reduction process on a first logical chunk of data stored in the vLUN at a first LCA and associated with a first PCA, wherein the first logical chunk has a size that is a nonzero integer multiple of the size of the storage extent; remap the first LCA to a second PCA in the second region, such that the first PCA in the first region is no longer required for storage of the first logical chunk of data and is therefore a first unneeded chunk; and instruct the thinly provisioned mapped LUN to deallocate the first [d]PCA associated with the first unneeded chunk.