The CA-Disk Rebuild utility can be used when things go wrong with archive tape volumes. The utility usually sits in a corner gathering dust - until a tape gets purged from the FILES data set or an archived data set gets purged right before you need to restore an older copy, at which point the utility gets fired up to save the day.
Previously, a Rebuild was an all-or-nothing proposition. If all you wanted was to restore one data set off the tape, you still had to rebuild the entire tape. Which meant - either purge the tape off the live FILES data set and Rebuild into the FDS, or create a temporary FILES data set and Rebuild into the FDS, then Restore the data set and delete the temporary FILES data set - a hassle either way.
With the release of enhancement PTF QO80272, Rebuild changes dramatically. This enhancement introduces the ability to selectively Rebuild Archive Data sets. Two new parameters, DSNAMES and FILENOS, have been added to the REBUILD command which allow you to select which archived data sets should have DSNINDEX entries, created by either a dsname pattern or a file sequence number.
Of the selected data sets on the Archive data set, only those that do not have a DSNINDEX will have a new one created. Existing DSNINDEX records will not be replaced.
In addition, an Archive data set doesn't need to be purged, to be selectively rebuilt. The current ARCHVOLS entry will be used if the Archive data set is already defined in the FILES data set, with some fields being updated to reflect the additional data sets now defined and other fields refreshed. The ARCHVOLS entry will be created if there currently isn't one.
A selective Rebuild still needs to read the entire tape, so won't necessarily run faster with selecting individual data sets. One function allows Rebuild to check all of the entries to be rebuilt, mostly to be able to refresh the information in the ARCHVOLS entry.
There is also the existing function to Rebuild only the ARCHVOLS entry, in the case where just the ARCHVOLS entry was deleted. This is sometimes done when an original tape is damaged and a copy is made (or available) so an ARCONLY Rebuild with the ARCKEY parameter can be done to change the DSNINDEX entries, thus they now refer to the new Archive data set. The ARCKEY parameter should specify the original tape volser or disk archive key.