IBM SC34-7012-01 manual Backup-while-open BWO, BWO and concurrent copy, BWO and backups

Chapter 18. Backup-while-open (BWO)

The BWO facility, together with other system facilities and products, allows you to take a backup copy of a VSAM data set while it remains open for update.

Many CICS applications depend on their data sets being open for update over a long period of time. Normally, you cannot take a backup of the data set while the data set is open. Thus, if a failure occurs that requires forward recovery, all updates that have been made to the data set since it was opened must be recovered. This means that you must keep all forward recovery logs that have been produced since the data set was opened. A heavily used data set that has been open for update for several days or weeks might need much forward recovery.

Using BWO, only the updates that have been made since the last backup copy was taken need to be recovered. This could considerably reduce the amount of forward recovery that is needed.

BWO and concurrent copy

Concurrent copy improves BWO processing by eliminating the invalidation of a BWO dump because of updates to the data set.

The following is a comparison of various kinds of dumps that you can request:

vNormal dump. Use of the data set must be quiesced so that serialization is obtained, the data set is dumped, and serialization is released. The data set cannot be used for the entire time.

vConcurrent copy dump. Use of the data set must be quiesced so that serialization is obtained, concurrent copy utilization is completed within a very short time (compared with the actual time to dump the data set), serialization is released, and the data set is dumped. The data set can be used after concurrent copy initialization is complete.

vBWO dump. Serialization is attempted but is not required, and the data set is dumped. If it is eligible for BWO, the data set is dumped without serialization and can remain in use for the entire time, but the dump can be invalidated by update activity to the data set.

vBWO dump using concurrent copy. Serialization is attempted but is not required, concurrent copy initialization is completed, and the data set is dumped. If it is eligible for BWO, the data set is dumped without serialization and can remain in use for the entire time, and updates that occur do not cause the dump to be invalidated.

To use concurrent copy, specify the CONCURRENT keyword when you use

DFSMShsm to dump BWO data sets.

BWO and backups

The BWO function allows backups to be taken by DFSMSdss when applications are running in continuous operation while the data set is open for update with full data integrity of copied data.

Continuous operation is typically 24 hours-a-day for five to seven days a week. This is feasible only for CICS VSAM file control data sets for which CICS creates

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