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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 83 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 47 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 class 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:
HPSS Installation Guide July 2008
Release 6.2 (Revision 2.0) 41