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.