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storage class by periodically extracting this information from the HPSS Core Server. Based upon
parameters in the purge policy, a purge run will be started when appropriate. The administrator can
also force the start of a purge run via SSM.
The disk purge is controlled by several parameters:
• 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 Start purge when space used reaches <nnn> percent parameter allows the amount of
free space that is maintained in a disk storage class to be controlled. 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 the amount of
free space that is maintained in a disk storage class to be controlled. The purge run will
attempt to create this amount of free space. Once this target is reached, the purge run will end.
• The Purge Locks expire after <nnn> minutes parameter allows the length of time a file can
be “purge locked” before it will appear on the MPS report to be controlled. 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 locked files after they expire. HPSS reports the fact that they have expired in the MPS
report.
• 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 their migration time. 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.
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.
3.9.3. Accounting Policy and Validation
The purpose of the Accounting Policy is to describe how a site will charge for storage, and, in
addition, to describe the level of user authorization (validation) to be 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 their style of accounting by writing an accounting site policy module for
the Gatekeeper.
If a site chooses Site-style accounting and Account Validation is turned off, LDAP must be used as
the authorization mechanism. The hpssGECOS field which is maintained for each user in LDAP,
contains the account index which allows Site-style accounting to be used. However if Account
Validation is turned on then the account index comes from the Account Validation metadata (through
the Gatekeeper).
If UNIX authorization is used and Account Validation is turned off, UNIX-style accounting must be
used because there is no hpssGECOS field. The basic limitation is that if the account index is needed
HPSS Installation Guide July 2008
Release 6.2 (Revision 2.0) 96