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This is part five of the series that began with
What is System-Managed Storage?.
What is availability management?
Availability management ensures that a recent copy of your DASD data sets exists. The purpose is to ensure that lost or damaged data sets can be retrieved at the correct level. To do this, availability management should automatically and periodically:
- copy data sets from DASD to tape volumes
- copy changed data sets on DASD volumes either to other DASD or tape volumes
- By performing these functions, availability management can help:
- guard against users accidentally losing or incorrectly changing data sets
- recover data after a volume is lost due to a hardware failure
- protect against loss of data due to a disaster
- ensure data which must be kept due to external requirements is retained (e.g. tax records)
What can DFSMShsm do for me?
DFSMShsm is a component of DFSMS/MVS which provides the following availability management functions:
| Automatic physical full-volume dump |
You can use full-volume dump to copy all data from a DASD volume to tape volumes automatically. This helps expedite recovery when an entire volume is lost or damaged and supplements the incremental recovery process. |
| Automatic incremental backup |
You can use incremental backup to copy data sets to daily backup volumes automatically, allowing you to maintain copies of data sets in case of damage to or loss of the originals. |
| Automatic control data set backup |
Backing up the DFSMShsm control data sets allows you to maintain copies of them in case of damage and allows DFSMShsm processing to continue uninterrupted. |
| Command dump and backup |
These functions are similar to automatic dump and backup, except that they are initiated by a command rather than occurring automatically. |
| Expiration of backup versions |
You invoke this function to clean up excess or unwanted backup versions of data sets in order to reduce the accumulation of backup versions. |
| Disaster backup |
You can create duplicate tapes from backup and migration level 2 volumes. The duplicates can be sent to off site to protect against damage to the computer site that would interfere with the continued operation of your business. |
| Aggregate backup and recovery |
You can back up a user-defined group of data sets for recovery at another site or at the same site. This allows you to recover complete entities, such as applications, in event of a disaster. |
| Backup-while-open |
You can allow SMS-managed VSAM data sets in use by CICS to be backed up while open. An exit is also provided to allow you to back up open SMS- and non-SMS-managed data sets without serialization. This allows you to backup data sets that are open all the time.
In addition, record level sharing provides a method of opening data sets using the Coupling Facility to manage serialization which allows data sets to be backed up while open.
| | Backup retry |
This is an option which allows you to specify that the system should delay backing up TSO data sets which are open and retry later. |
What can DFSMSdss do for me?
DFSMSdss is a component of DFSMS/MVS which works with DFSMShsm to provide the following availability management functions:
| Concurrent copy |
This hardware and software solution allows you to back up a data base or collection of data at a point in time with minimum down time for the data. The data is unavailable only long enough for DFSMSdss to initialize a concurrent copy session, a small fraction of the time the complete backup takes. |
| Logical data set dump |
Backs up data sets as logical entities. Because the environment at a remote site may differ from your environment, this is recommended for disaster backup, as it allows data to be restored to unlike devices. |
| Logical volume dump |
Allows you to perform a logical backup of an entire volume. You must use this type of backup if you need the ability to restore the data to an unlike device |
| Physical data set dump |
Backs up a track-level image of the data set. This should only be used if backup copies will be used at the site where the backup was done and the data will be restored to the same device type. |
| Physical volume dump |
Allows you to backup a track-level image of the volume to tape. This type of dump can only be restored on the same type of device from which it was dumped. |
Why should I use system-managed storage?
Without system-managed storage, you must set some availability management parameters individually for each volume you want managed. You can set others only for the system as a whole. Therefore, availability management for data sets is based on the parameters for the volumes on which they happen to reside.
With system managed storage, you can establish an entire SMS storage group as a candidate for automatic dump. There is no need to issue special commands to set the necessary parameters; the necessary information is contained in the SMS configuration.
In addition, because data sets are managed at the data set level based on their management classes, data sets with availability management requirements can coexist on the same volumes. Data with different dump and expiration requirements need not be segregated by volume.
In summary
DFSMS/MVS provides the key to system-managed storage in an MVS environment. Using a combination of storage group and management class, you can define a data set level policy for availability management. The system can then automatically back up and dump data sets and volumes. This can help improve data availability and help reduce the number of disruptions caused by hardware failures or accidental data set deletion or damage.
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