Append to media question - tape

[Nick_Zulli]

Assume this:

Perform an inventory

Have only one tape inserted into an auto loader

That tape is half full of old data

Data is past the overwrite protection window

Pre-scan is not enabled

When does a job determine to overwrite or append when the option to “Append to media, overwrite if no appendable media is available” is selected? 

1)

Does it first wind the tape to the end of the old dataset and “append” from that point and if needed, wind the tape again to the beginning of the old data and then perform the “overwrite”?

2)

Due to the inventory process does it know how old the data is on the tape and just perform the overwrite not even attempting to perform an append job?

3)

Does it wind the tape to the end of the old dataset and “append” from that point and if needed, ask for additional media not going back to overwrite the old data?

4)

Other…

I ask because we run incremental during the week and most of the time we can fit the data onto a single LTO 3 tape.  But once and a while it asks for a second tape.  The strange thing is that it asks when only 140GB (before compression) is written to the tape.  The tapes are recycled every week so there is old data on them.  I do not see hard/soft errors on the media or drive.

Thanks for your background on this.

[Kiran_Bandi]

It depneds upon the appendable period setting also, if the tape is not overwritable.

As it is a overwirtable media, BE overwrite it with the new data.

Coming to your problem, is compression enabled in the backup job? You may be backing up already compressed data. Disable compression in the backup job and see. 

Regards...

EDIT: If there was a media which was half full and appendable but not overwritable. BE may used that media to start incremental job. As it is not enough to complete the job it could have requested for another.

[Ken_Putnam]

When does a job determine to overwrite or append when the option to “Append to media, overwrite if no appendable media is available” is selected?

If the Job is defined as Append, else Overwrite, Backup Exec will check the catalog to see if the tape volume is past the APP period, if so the job becomes an overwrite, and since the tape is past the OPP, then it will start writing at the beginning of the tape

If it is within the APP, then BackupExec  will FastForward until itreaches the End-of-Data marker and begin writing at that point

Does it first wind the tape to the end of the old dataset and “append” from that point and if needed, wind the tape again to the beginning of the old data and then perform the “overwrite”?

Whan an Append operation reaches the end of a tape volume, it will only continue as an Overwrite on a new tape volume.  If it rewound and then started writing at the begining of the 1st volume, this would essentially be a Quick Erase, and all data written to that point would be lost