We are running an ADSM 3.1.2.0 server under MVS. Client backups are sent
directly to tape. Each time a tape volume fills up, the ADSM client output
reports that the backup of the file in progress is unsuccessful, and that the
backup is being retried. When the file is big enough for the client to show a
percent completion indication, the percentage goes back to zero at the
beginning of the retry and then increments at about the same rate as it did
before the retry. We recently took a close look at statistics and volume
contents for a specific backup. The statistics showed 5.7 gigabytes of data
backed up and 6.7 gigabytes of data transferred over the network. Each file in
progress when a tape filled up was split between the volume that filled up and
the next volume mounted. The aggregate size of the split files was about two
gigabytes. I don't know of a practical way to determine the aggregate size of
the first segments of the files, but I would expect this to be about half of
the the aggregate size of the files. These statistics and the client output
suggest that the following sequence of events occurs when a tape fills up:

1.The client sends data until the tape fills
2.The client detects a failure in the backup
3.The server mounts a new tape
4.The client restarts transmission at the beginning of the file
5.The server discards the incoming data that duplicates data already written
to tape
6.The remaining data is written to the new tape

Can anyone confirm or refute this suspicion? If this suspicion is correct, is
there any way to eliminate the unnecessary retransmission of data?