DFSMShsm maintains backup copies as active backup copies and retained
backup copies. Active copies are the backup copies that have not yet
rolled off. Retained copies are the backup copies that have rolled
off from the active copies, but have not yet reached their retention
periods. DFSMShsm can maintain a maximum of 100 active copies. DFSMShsm
can maintain more than enough retained copies for each data set to
meet all expected requirements.
Roll-off processing occurs when the number of existing active copies
exceeds the maximum number of active backup versions, as defined by
the management class attribute Number of backup versions (data exists)
for SMS-managed data sets, and the value of the SETSYS VERSIONS command,
for non SMS-managed data sets. When a new backup version causes the
maximum number of active copies to be exceeded, DFSMShsm checks all
of the active copies to see if any active copy has retained days specified,
and if the retained days value is met. The active backup copies are
then rolled off in the following order:
- Roll-off processing removes all backup versions that have expired
RETAINDAYS values.
- If at least one active backup copy has retain days specified,
but none of the active backup copies have met their retain days:
- The oldest active backup copy is rolled-off if it does not have
a RETAINDAYS value specified.
- If the oldest active backup copy has RETAINDAYS value specified,
then the oldest copy is replaced by the new backup copy, and the replaced
active copy is maintained as a retained backup copy.
- If none of the active backup copies have RETAINDAYS values specified,
the excess versions are deleted, starting with the oldest version.
The maximum number of active backup copies is 100.
When an active backup copy is rolled off from the active copies,
but has not yet reached its retention period, DFSMShsm maintains it
as a retained backup copy. DFSMShsm can maintain more than enough
retained copies for each data set to meet all expected requirements.
Generation and version numbers are not associated with retained copies
and cannot be used to recover them. You can recover retained copies
only by specifying the date, and optionally time, that the version
was created.
Example 1
The following example illustrates roll-off processing when several
backup versions of a data set have met their retention periods. Assume,
that:
- the maximum number of active backup versions is 3,
- the data set is cataloged,
- 3 data set backup versions are already created.
Table 1. The state of the data set backup versions just before
the fourth data set backup version is created on October 31st.Version number |
Date created |
RETAINDAYS value |
RETAINDAYS specified at backup time |
RETAINDAYS met indicator on Oct 31st |
Version 3 |
Oct 30th |
1 |
Yes |
Met |
Version 2 |
Oct 29th |
2 |
Yes |
Met |
Version 1 |
Oct 28th |
0 |
No |
N/A |
Table 2. The state of data set backup versions after roll-off processing
completes. The second and the third versions rolled offVersion number |
Date created |
RETAINDAYS value |
RETAINDAYS specified at backup time |
RETAINDAYS met indicator on Oct 31st |
Version 4 |
Oct 31st |
31 |
Yes |
Not met |
Version 1 |
Oct 28th |
0 |
No |
N/A |
Example 2
The following example illustrates roll-off processing for active
copies with retention periods that have not been met. Assume that:
- the maximum number of active backup versions is 3,
- the data set is cataloged,
- 3 data set backup versions are already created.
Table 3. The state of data set backup versions just before the
fourth data set backup version is created on October 31st.Version number |
Date created |
RETAINDAYS value |
RETAINDAYS specified at backup time |
RETAINDAYS met indicator on Oct 31st |
Version 3 |
Oct 30th |
400 |
Yes |
Not met |
Version 2 |
Oct 29th |
400 |
Yes |
Not met |
Version 1 |
Oct 28th |
400 |
Yes |
Not met |
Table 4. The state of data sets after roll-off processing is complete.
The oldest version rolled-off and became a retained backup copy.Version number |
Date created |
RETAINDAYS value |
RETAINDAYS specified at backup time |
RETAINDAYS met indicator on Oct 31st |
Version 4 |
Oct 31st |
400 |
Yes |
Not met |
Version 3 |
Oct 30th |
400 |
Yes |
Not met |
Version 2 |
Oct 29th |
400 |
Yes |
Not met |
Table 5. Retained backup copies after roll-off processing completes.Version number |
Date created |
RETAINDAYS value |
RETAINDAYS specified at backup time |
RETAINDAYS met indicator on Oct 31st |
N/A |
Oct 28th |
400 |
Yes |
Not met |