US Patent 7546432 Pass-through write policies of files in distributed storage management

A hierarchical storage system includes file servers and a policy engine server. Offline attributes are added to file system inodes in a primary file server, file system parameters are added in the primary server, offline read and write access method fields are added to a connection database, and the primary file server uses these attributes and parameters for selecting a particular read method or write method for access to an offline file or section of an offline file. The write methods follow a “write recall full” policy, a “pass-through write” policy, a “pass-through multi-version” policy, or a “directory write pass-through” policy. The pass-through multi-version policy results in a new offline version of a file each time that a client opens and writes to a multi-version file. The directory write pass-through policy results in a new offline file when a file is created within a write pass-through directory.