Concurrent copy improves backup-while-open processing by significantly reducing the chances of the invalidation of a backup-while-open dump because of updates to the data set. To use concurrent copy, specify the CONCURRENT keyword when you dump backup-while-open data sets. The following is a comparison of the various kinds of dumps you can ask for:

• Normal dump. Use of the data set must be quiesced. DFSMSdss obtains serialization, dumps the data set, and then releases the serialization. The data set cannot be used for the entire time.
• Concurrent copy dump. Use of the data set must be quiesced. DFSMSdss obtains serialization, performs concurrent copy initialization, releases serialization, and then dumps the data set. DFSMSdss completes concurrent copy initialization within a very short time (compared to the actual time to dump the data set). DFSMSdss can use the data set as soon as the concurrent copy initialization is complete.
• Backup-while-open dump. Use of the data set does not need to be quiesced. DFSMSdss dumps the data set without obtaining serialization. The data set can remain in use for the entire time, but update activity can invalidate the dump at any time during the dump.
• Backup-while-open dump using concurrent copy. Use of the data set does not need to be quiesced. DFSMSdss does not obtain serialization. DFSMSdss performs the concurrent copy initialization. DFSMSdss completes concurrent copy initialization within a very short time (compared to the actual time to dump the data set). The data set can remain in use for the entire time. Like the Backup-while-open dump, update activity during the dump can invalidate the dump. However, only update activity that occurs before DFSMSdss performs the concurrent copy initialization can invalidate the dump. The chances of the update activity invalidating the dump are significantly reduced because the concurrent copy initialization completes very quickly.