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Chapter 2 HPSS Planning
HPSS Installation Guide September 2002 85
Release 4.5, Revision 2
• The Start purge when space used reaches <nnn> percent parameter allows sites control
over the amount of free space that is maintained in a disk storage class. A purge run will
be started for this storage class when the total space used in this class exceeds this value.
• The Stop purge when space used falls to <nnn> percent parameter allows sites control
over the amount of free space that is maintained in a disk storage class. The purge run will
attempt to create this amount of free space. Once this target is reached, the purge run will
end.
• The Do not purge files accessed within <nnn> minutes parameter determines the
minimum amount of time a site wants to keep a file on disk. Files that have been accessed
within this time interval are not candidates for purge.
• The Purge by list box allows sites to choose the criteria used in selecting files for purge. By
default, files are selected for purge based on the creation time of their purge record.
Alternately, the selection of files for purging may be based on the time the file was created
or the time the file was last accessed. Files may be purged in an unpredictable order if this
parameter is changed while there are existing purge records already in metadata until
those existing files are processed.
• The Purge Locks expire after <nnn> minutes parameter allows sites to control how long
a file can be purge locked before it will appear on the MPS report as an expired purge lock.
The purge lock is used to prevent a file from being purged from the highest level of a
hierarchy. Purge locks only apply to a hierarchy containing a disk on the highest level.
HPSS will not automatically unlock purge locked files after they expire. HPSS simply
reports the fact that they have expired in the MPS report.
Administrators should experiment to determine the parameter settings that will fit the needs of
their site. If a site has a large amount of disk file write activity, the administrator may want to have
more free space and more frequent purge runs. However, if a site has a large amount of file read
activity, the administrator may want to have smaller disk free space and less frequent purge runs,
and allow files to stay on disk for a longer time.
A purge policy must not be defined for a tape storage class or a storage class which does not
support migration.
2.8.3 Accounting Policy and Validation
The purpose of the Accounting Policy is to describe how the site will charge for storage usage as
well as the level of user authorization (validation) performed when maintaining accounting
information.
A site must decide which style of accounting to use before creating any HPSS files or directories.
There are two styles of accounting: UNIX-style accounting and Site-style accounting. In addition a
site may decide to customize the style of accounting used by writing an accounting site policy
module for the Gatekeeper.
The metadata for each file and directory in the HPSS system contains a number, known as an
account index, which determines how the storage will be charged. Each user has at least one
account index, known as their default account index, which is stamped on new files or directories
as they are created.