Hub/Switch Installation Guide

Chapter 2 HPSS Planning
92 September 2002 HPSS Installation Guide
Release 4.5, Revision 2
to determine HPSS hardware requirements and determine how to configure this hardware to
provide the desired HPSSsystem. Theprocess of organizing the available hardware into a desired
configuration results in the creation of a number of HPSS metadata objects. The primary objects
created are classes of service, storage hierarchies, and storage classes.
A Storage Class is used by HPSS to define the basic characteristics of storage media. These
characteristics include the media type (the make and model), the media block size (the length of
each basic block of data on the media), the transfer rate, and the size of media volumes. These are
the physical characteristics of the media. Individual media volumes described in a Storage Class
are called Physical Volumes (PVs) in HPSS.
Storage Classes also define the way in which Physical Volumes are grouped to form Virtual
Volumes (VVs). Each VV contains one or more PVs. The VV characteristics described by a Storage
Class include the VV Block Size and VV Stripe Width.
A number of additional parameters are defined in Storage Classes. These include migration and
purge policies, minimum and maximum storage segment sizes, and warning thresholds.
An HPSS storage hierarchy consists of multiple levels of storage with each level represented by a
different Storage Class. Files are moved up and down the storage hierarchy via stage and migrate
operations, respectively, based upon storage policy, usage patterns, storage availability, and user
requests.If data is duplicatedfor a file atmultiple levels in thehierarchy, the more recentdata is at
the higher level (lowest level number) in the hierarchy. Each hierarchy level is associated with a
single storage class.
Class ofService (COS) is an abstraction of storage systemcharacteristics that allows HPSS users to
select a particular type of service based on performance, space, and functionality requirements.
Each COS describes a desired service in terms of such characteristics as minimum and maximum
file size, transfer rate, access frequency, latency, andvalidread or write operations. A file residesin
a particular COS and the COS is selected when the file is created. Underlying a COS is a storage
hierarchy that describeshow data forfiles in that class are tobe stored in theHPSS system. A COS
can be associated with a fileset such that all files created in the fileset will use the same COS.
A file family is an attribute of an HPSS file that is used to group a set of files on a common set of
tape virtual volumes. HPSS supports grouping of files only on tape volumes. In addition, families
can only bespecified by associating afamily with a fileset, andcreating thefile in the fileset.When
a file is migrated from disk to tape, it is migrated to a tape virtual volume assigned to the family
associated with the file. If no family is associated with the file, the file is migrated to the next
availabletapenotassociatedwith afamily(actuallytoatapeassociatedwith familyzero).Ifthefile
is associated with a family and no tape VV is available for writing in the family, a blank tape is
reassigned from family zero to the file’s family. The family affiliation is preserved when tapes are
repacked.
The relationship between storage class, storage hierarchy, and COS is shown in Figure 2-2.