Storage tiering uses file system awareness of storage class for storage allocation or migration of a storage object from one class of storage to another. For example, the storage object is a production file system, a logical unit number (LUN) of storage, or a snapshot copy of the production file system or LUN. Each storage class may comprise a different back-end disk type, such as Fiber Channel, ATA, etc. Storage allocation or migration is based on storage class to implement a storage policy, such as: (a) move snapshots off the class of storage of the production object and onto a different class of storage; (b) direct new writes to a specified class of storage; or (c) writes targeting a particular storage object are targeted to a particular class of storage.