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Chapter 1 HPSS Basics
22 September 2002 HPSS Installation Guide
Release 4.5, Revision 2
1.3.1 HPSS Files, Filesets, Volumes, Storage Segments and Related Metadata
The components used to define the structure of the HPSS name space are filesets and junctions. The
components containing user data include bitfiles, physical and virtual volumes, and storage
segments. Components containing metadata describing the attributes and characteristics of files,
volumes, and storage segments, include storage maps, classes of service, hierarchies, and storage
classes.
• Files (Bitfiles). Files in HPSS, called bitfiles in deference to IEEE Reference Model
terminology, are logical strings of bytes, even though a particular bitfile may have a
structure imposed by its owner. This unstructured view decouples HPSS from any
particular file management system that host clients of HPSS might have. HPSS bitfile size
is limited to 2 to the power of 64 minus 1 (2
64
- 1) bytes.
Each bitfile is identified by a machine-generated name called a bitfile ID. It may also have
a human readable name. It is the job of the HPSS Name Server (discussed in Section 1.3.2)
to map a human readable name to a bitfile's bitfile ID. By separating human readable
names from the bitfiles and their associated bitfile IDs, HPSS allows sites to use different
Name Servers to organize their storage. There is, however, a standard Name Server
included with HPSS.
• Filesets. A fileset is a logical collection of files that can be managed as a single
administrative unit, or more simply, a disjoint directory tree. A fileset has two identifiers:
a human readable name, and a 64-bit integer. Both identifiers are unique to a given DCE
cell.
• Junctions. A junction is a Name Server object that is used to point to a fileset. This fileset
may belong to the same Name Server or to a different Name Server. The ability to point
junctions allows HPSS users to traverse to different Storage Subsystems and to traverse to
different HPSS systems via the Federated Name Space. Junctions are components of
pathnames and are the mechanism which implements this traversal.
• File Families. HPSS files can be grouped into families. All files in a given family are
recorded on a set of tapes assigned to the family. Only files from the given family are
recorded on these tapes. HPSS supports grouping files on tape volumes only. Families can
only be specified by associating the family with a fileset. All files created in the fileset
belong to the family. When one of these files is migrated from disk to tape, it is recorded on
a tape with other files in the same family. If no tape virtual volume is associated with the
family, a blank tape is reassigned from the defaultfamily. The family affiliation ispreserved
when tapes are repacked.
• Physical Volumes. A physical volume is a unit of storage media on which HPSS stores
data. The media can be removable (e.g., cartridge tape, optical disk) or non-removable
(magnetic disk). Physical volumes may also be composite media, such as RAID disks, but
must be represented by the host OS as a single device.
Physical volumes are not visible to the end user. The end user simply stores bitfiles into a
logically unlimited storage space. HPSS, however, must implement this storage on a
variety of types and quantities of physical volumes.
For a list of the tape physical volume types supported by HPSS, see Table 2-4: Suggested
Block Sizes for Tape on page 99.