Why is my job not appending data to my tapes?
Created: 12 Dec 2011 • Updated: 14 May 2012
Question: Why is my job not appending data to my tapes?
Answer: There are a couple of reasons why jobs do not append data to tapes.
1) The job is set to overwrite.
To append data to tapes, the job must be set to either of the two append option. See the figure below
2) The job will only append to the first tape.
A job can only append to the first tape that it writes to. When that tape is full, it will require an overwriteable tape. It cannot append to the second or subsequent tapes. This is by design and there is no way to change this behaviour.
3) The append period is too short.
The append period is calculated from the START of the first job that over-writes the tape. The append period is not extended after this. Suppose the append period is set to 5 hours and the first job that over-writes the tape takes 6 hours to complete. By the time the job completes, the tape is no longer appendable.
4) The jobs overlap.
By job overlap, I mean; while the first job is running, the second job starts.
When a job is running, the tape is marked as unappendable because the end-of-file marker is not written. If a job starts while the first job is running, then it will not be able to find an appendable media. It will then switch to overwrite mode, if the job property is set to "Append, overwrite if if no appendable media is available", or it will fail if it is set to "Append, terminate job if no appendable media is available". For the first append option even when the job finally finishes waiting and start, it will use an overwriteable media and will not switch back to the append mode.
The only solution for this situation is to schedule your jobs in such a way that there is no overlap.
Question: What about disk media?
Answer: The above is also applicable to disk media. However, for disk media, there is no advantage to appending to a media. For tape, you append data to them to maximise the use of the tape capacity. For disk, you can use as much or as little disk space as you require, provided you have not set the B2D folder property to allocate the maximum size for the .bkf files. By appending to a disk media, you would extend the overwrite protection period of that media and thus preventing it from being recycled earlier. For example, your first job creates a .bkf file and the overwrite protection period is 3 days. On the 4th day, this .bkf can be overwritten and the disk space occupied by it is re-used. However, if there is a second job the next day which appends to this file, then the .bkf will only be overwriteable on the 5th day. Thus the space occupied by the data from the first job is locked up for another day before it can be overwritten.
This is why you should always set your jobs to Overwrite if you are writing to disk media.