Backup volume spill process

Moving backup versions from DASD backup volumes to spill volumes is called spill. Spill is a process that applies only if you are using DASD devices to store your backup versions. If you use DASD as your daily backup volumes, your daily backup volumes eventually become filled with recent backup versions and older backup versions of the same data sets. The DASD daily backup volumes can also contain backup versions of deleted data sets and retired backup versions.
Note: Although both the spill and recycle process output to spill backup tapes, the spill process occurs only from DASD. Moving backup versions from tape backup volumes is part of recycle.

When adding DASD backup volumes to DFSMShsm with an ADDVOL command, you can specify a maximum percentage of the capacity of the volume above which the volume is considered to be full after spill or cleanup processing. This percentage is called the threshold of occupancy. When a DASD daily backup volume becomes full (an allocation has been failed for lack of space), it is spilled by the spill process. If the spill process does not reduce the occupancy of the volume below the threshold of occupancy, the volume is still considered to be full.

The spill process moves all but the latest backup version of a data set from a DASD daily backup volume to a spill backup volume. DFSMShsm owns the spill backup volume. During daily backup volume selection when all DASD daily backup volumes are full, DFSMShsm uses the spill process to make space available on the full DASD daily backup volumes. The spill process produces a DASD daily backup volume usable during volume backup processing. The spill process moves the following from daily backup volumes to spill backup volumes:
  • All but the latest backup version of each data set
  • All retired backup versions (see Data set retirement)
  • All backup versions of a deleted data set

If a backup version is not valid, DFSMShsm does not move it. Instead, DFSMShsm scratches the invalid backup version.

DFSMShsm spills the full, unallocated, DASD daily backup volume that is assigned to the current day in the backup cycle and that has not been spilled in the longest period of time. If the volume spill process is successful, the DASD daily backup volume is used for the backup of the DFSMShsm-managed volumes. Otherwise, DFSMShsm spills the full, unallocated, DASD daily backup volume that has not been spilled in the next longest period of time. This process is repeated until a usable DASD daily backup volume is produced or until every full, unallocated, DASD daily backup volume assigned to the current day in the backup cycle has been spilled on that day.

If cataloged and uncataloged data sets have the same name and each has backup versions, DFSMShsm does not move either the latest backup version of the cataloged data set or the latest backup version of the uncataloged data set.

When a DASD daily backup volume is spilled, it is also cleaned up. Backup volume cleanup process contains detailed information about cleanup processing. When the full DASD daily backup volume to be spilled has been allocated, DFSMShsm:
  • Reads the volume table of contents (VTOC) of the DASD daily backup volume. As each data set VTOC entry is encountered, the name is checked to see if it is a backup version created by DFSMShsm. If it is, a check is made to see if this backup version is the latest backup version for the cataloged or uncataloged data set. If it is not the latest backup version, is a retired version, or is a version of a deleted data set and it is a valid backup version, DFSMShsm records that the backup version needs to be moved to a spill backup volume. If the data set on the backup volume either was not created by DFSMShsm or is a VTOC or VCAT copy, it is not processed.
  • Selects a spill backup volume if any backup versions exist that should be moved. After DFSMShsm selects a spill backup volume, it begins to move the backup versions.
  • Determines the percentage of allocated space on the daily backup volume after all the backup versions are moved to the spill backup volume. If the percentage of allocated space is less than or equal to the user-specified threshold of occupancy, the daily backup volume is no longer considered full and is used for the backup of the DFSMShsm-managed volumes. If the percentage of allocated space is not less than or equal to the threshold of occupancy, the daily backup volume is considered to still be full and is not selected as a target for backup versions. You can specify the threshold of occupancy by using the THRESHOLD parameter of the ADDVOL command.