Disk migration is controlled by several parameters. By default, these parameters are the same across all subsystems. However,
3.9.1.2. Migration Policy for Tape
There are two tape migration algorithms: tape file migration and tape volume migration. The algorithm which MPS applies to a given tape storage class is selected in the migration policy for that storage class.
The purpose of tape file migration is to make a second copy of files written on tape. This algorithm is similar to disk migration, but only a single additional copy is possible. It is also possible to configure tape file migration such that files are moved downwards in the hierarchy without keeping a second copy.
It is possible for tape file migration to make a second copy of files written on tape. The algorithm is similar to disk file migration, but only a single additional copy is possible. It is also possible to configure tape file migration such that files are moved downwards in the hierarchy without keeping a second copy.
The purpose of tape volume migration is to empty tape virtual volumes that have become full (reached EOM) and have significant unused space in them. Unused space on a tape volume is generated when files on that tape are deleted or overwritten. Since data can only be recorded on tapes sequentially, vacated recording space on tapes can be reclaimed only by moving all remaining files to other tapes.
Tape volume migration attempts to empty tapes by moving data off of the tapes to other volumes. When a tape becomes empty, it is a candidate for reuse. The reclaim utility program resets the state of the empty tape volumes so that they can be reused. The reclaim utility can be run from SSM, but it should generally be set up to run on a periodic basis via the cron facility. For more information on reclaim, see Section 8.1.5: Reclaiming HPSS Tape Virtual Volumes of the HPSS Management Guide and the reclaim manual page.
The repack utility can also be used to create empty tapes in a storage class. The administrator should determine whether a tape should be repacked based on the number of holes (due to file overwrite or deletion) on the tape. If a tape storage class is at the bottom of a hierarchy, repack and reclaim must be run periodically to reclaim wasted space. For more information on repack, see Section 8.1.4: Repacking Tape Virtual Volumes of the HPSS Management Guide and the repack manual page.
The migration policy parameters which apply to the different tape migration algorithms in detail in Section 6.4.2.3: Tape Migration Policy Configuration in the HPSS Management Guide.
3.9.2. Purge Policy
The purge policy allows the MPS to remove the bitfiles from disk after the bitfiles have been migrated to a lower level of storage in the hierarchy. A purge policy cannot be defined for a tape storage class or a disk storage class which does not support migration. Sites may or may not wish to define a purge policy for all disk storage classes that support migration. Purging from tapes is controlled by the "Migrate Files and Purge" flag of the tape migration policy; there is no separate purge policy for tape storage classes.
The specification of the purge policy in the storage class configuration enables the MPS to do the disk purging according to the purge policy for that particular storage class. Purge is run for a storage class on a demand basis. The MPS maintains current information on total space and free space in a
HPSS Installation Guide | July 2008 |
Release 6.2 (Revision 2.0) | 95 |
