HPSS Servers
HPSS servers include the Core Server, Migration/Purge Server, Gatekeeper, Location Server, Log Client, Log Daemon, Physical Volume Library, Physical Volume Repository, Mover, Storage System Management System Manager, and Startup Daemon. Figure 3: HPSS Components provides a simplified view of the HPSS system. Each major server component is shown, along with the basic control communication paths (thin arrowed lines). Infrastructure items (those components that “glue together” the distributed servers) are shown at the top of the cube.
Core Server. The Core Server provides several key sets of functionality.
First, the Core Server provides translation between human-oriented names and HPSS object identifiers. Name space objects managed by the Core Server are filesets, junctions, directories, files, hard links, and symbolic links. The Core Server provides access verification to objects and mechanisms for manipulating access to these objects via a Portable Operating System Interface (POSIX) view of the name space. This name space is a hierarchical structure consisting of directories, files, and links. These name space objects may exist within filesets that are connected via junctions.
Second, the Core Server provides the abstraction of logical bitfiles to its clients. A bitfile is identified by a Core Server generated name called a bitfile ID. Clients may reference portions of a bitfile by specifying the bitfile ID and a starting address and length. The Core Server supports random access to files and sparsely written files. It supports parallel reading and writing of data to bitfiles and performs the mapping of logical portions of bitfiles onto physical storage devices. The Core Server supports the migration, purging, and staging of data in a storage hierarchy (though the migration/purge policies are implemented through the Migration/Purge Server, a client to the Core Server).
Third, the Core Server provides a hierarchy of storage objects: storage segments, virtual volumes, and physical volumes. The Core Server translates storage segment references into virtual volume references and then into physical volume references, handles the mapping of physical resources into striped virtual volumes to allow parallel I/O to that set of resources, and schedules the mounting and dismounting of removable media through the Physical Volume Library (see below).
Migration/Purge Server (MPS). The MPS allows a site to implement its storage management policies by managing the placement of data on HPSS storage media using site-defined migration and purge policies. By making appropriate calls to its Core Server, an MPS copies data to lower levels in the hierarchy (migration), removes data from the current level once copies have been made (purge), or moves data between volumes at the same level (lateral move). Based on the hierarchy configuration, MPS can be directed to create duplicate copies of data when it is being migrated from disk or tape. This is done by copying the data to multiple lower levels in the storage hierarchy.
There are three types of migration: disk migration, tape file migration, and tape volume migration. The designation disk or tape refers to the type of storage class that migration is running against. See Section 3.7.2: Migration/Purge Server on page 72 for a more complete discussion of the different types of migration.
MPS runs migration on each storage class periodically using the time interval specified in the migration policy for that class. See Section 2.3.7: HPSS Policy Modules on page 34 for details on migration and purge policies. Migration runs can be started automatically when the warning or critical space thresholds for the storage class are exceeded. In addition, migration runs can be started manually by an administrator.
Purge runs are started automatically on each storage class when the free space in that class falls below the percentage specified in the purge policy. Purge runs may also be started manually.
Disk Migration/Purge: The purpose of disk migration is to make one or more copies of disk files to lower levels in the hierarchy. The number of copies depends on the configuration of the hierarchy. For disk, migration and purge are separate operations. It is common for disk storage classes which have been configured for migration to also be configured for purge as well. Once a file has been migrated (copied) downwards in the hierarchy, it becomes eligible for purge, which subsequently removes the file from the higher level and allows the disk space to be reused.
Tape File Migration: The purpose of tape file migration is to make an additional copy (or multiple additional copies) of a file, in a tape storage class, to a lower level in the hierarchy. It is also possible to move files downwards instead of copying them. In this case there is no duplicate copy maintained. There is no separate purge component to tape file migration. Empty volumes must be reclaimed using the reclaim utility.
Tape Volume Migration: The purpose of tape volume migration is to free tape volumes for reuse. Tape volumes are selected based on being in the EOM map state and containing the most unused space (caused by users overwriting or deleting files). The remaining segments on these volumes are either migrated downwards to the next level in the hierarchy, or are moved laterally to another tape volume at the same level. This results in empty tape volumes which may then be reclaimed. Note that there is no purge component to tape volume migration. All of the operations use a move instead of a copy semantic.