Chapter 2 HPSS PlanningHPSS Installation Guide September 2002 85Release 4.5, Revision 2• The Start purge when space used reaches percent parameter allows sites controlover the amount of free space that is maintained in a disk storage class. A purge run willbe started for this storage class when the total space used in this class exceeds this value.• The Stop purge when space used falls to percent parameter allows sites controlover the amount of free space that is maintained in a disk storage class. The purge run willattempt to create this amount of free space. Once this target is reached, the purge run willend.• The Do not purge files accessed within minutes parameter determines theminimum amount of time a site wants to keep a file on disk. Files that have been accessedwithin 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. Bydefault, 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 createdor the time the file was last accessed. Files may be purged in an unpredictable order if thisparameter is changed while there are existing purge records already in metadata untilthose existing files are processed.• The Purge Locks expire after minutes parameter allows sites to control how longa 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 ahierarchy. 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 simplyreports the fact that they have expired in the MPS report.Administrators should experiment to determine the parameter settings that will fit the needs oftheir site. If a site has a large amount of disk file write activity, the administrator may want to havemore free space and more frequent purge runs. However, if a site has a large amount of file readactivity, 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 notsupport migration.2.8.3 Accounting Policy and ValidationThe purpose of the Accounting Policy is to describe how the site will charge for storage usage aswell as the level of user authorization (validation) performed when maintaining accountinginformation.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 asite may decide to customize the style of accounting used by writing an accounting site policymodule for the Gatekeeper.The metadata for each file and directory in the HPSS system contains a number, known as anaccount index, which determines how the storage will be charged. Each user has at least oneaccount index, known as their default account index, which is stamped on new files or directoriesas they are created.
