1. A computer readable medium comprising software instructions that, when executed, perform a method for preserving data stored in a file system comprising a plurality of files, comprising: determining whether storage capacity of the file system has reached a threshold level, wherein the threshold level is stored in at least one of a plurality of size-reducing policies; obtaining at least one criterion from the at least one size-reducing policy; identifying a subset of the plurality of files that match the at least one criterion; accessing metadata of each of the identified subset of files, wherein the metadata of each of the identified subset of files comprises at least one option for reducing a size of the file; and performing a size-reducing action to reduce a size of each of the identified subset of files based on the at least one option for reducing the size of each of the identified subset of files and the at least one criterion.