A system comprising: a file system; a volume system configured to expose up a volume to the file system in a manner that the volume is exposed with a plurality of tiers (212A-212D), each tier (212A-212D) comprising storage having a distinct trait set and being a set of one or more regions of the volume having a common trait set; a plurality of underlying storage systems to support the traits set for each of the plurality of tiers (212A-212D) of the volume; a mapping system configured to map logical address locations of the volume to the plurality of underlying storage systems to support the trait set for each of the plurality of tiers (212A-212D) of the volume; and wherein the file system is configured to cause a file system namespace item or a file fragment to be stored in a particular tier (212A-212D) of the plurality of tiers (212A-212D) based on storage traits to be applied to the file system namespace item, each of the storage traits being either a mandatory or an optional storage trait as expressly stated by a user, and wherein the storage traits of the file system namespace item are consistent with the trait set of the particular tier (212A-212D); and wherein the file system includes a tier engine, configured to monitor file system storage trait sets dynamically and to perform this monitoring continuously, periodically, and/or in response to events for multiple file system namespace items and multiple file fragments, and further configured to move the file system namespace item from the particular tier (212A-212D) to a target tier (212A-212D) in response to monitoring changing storage traits of the file system namespace item. a file system; a volume system configured to expose up a volume to the file system in a manner that the volume is exposed with a plurality of tiers (212A-212D), each tier (212A-212D) comprising storage having a distinct trait set and being a set of one or more regions of the volume having a common trait set; a plurality of underlying storage systems to support the traits set for each of the plurality of tiers (212A-212D) of the volume; a mapping system configured to map logical address locations of the volume to the plurality of underlying storage systems to support the trait set for each of the plurality of tiers (212A-212D) of the volume; and wherein the file system is configured to cause a file system namespace item or a file fragment to be stored in a particular tier (212A-212D) of the plurality of tiers (212A-212D) based on storage traits to be applied to the file system namespace item, each of the storage traits being either a mandatory or an optional storage trait as expressly stated by a user, and wherein the storage traits of the file system namespace item are consistent with the trait set of the particular tier (212A-212D); and wherein the file system includes a tier engine, configured to monitor file system storage trait sets dynamically and to perform this monitoring continuously, periodically, and/or in response to events for multiple file system namespace items and multiple file fragments, and further configured to move the file system namespace item from the particular tier (212A-212D) to a target tier (212A-212D) in response to monitoring changing storage traits of the file system namespace item.