I think you are just appending to the media and not overwriting it. Create a restore job and see whether you can see the previous day's backup.
Your current OPP will retain data forever. This means that your disk will eventually fill up and you would have a out of space problem. If you want to retain data for 2 months, the longest period you should set your OPP is 2 months. However you also need to calculate the size of each of your backup and how many backups you would create in 2 months. Your disk is 6TB. If your daily backup is 1TB, you would run out of disk space in 6 days, so you have to think about getting another disk, etc. It is no point just setting the OPP to 2 months, you would just get a out-of-disk space situation. If you want to use just 1 disk, then you would have to shorten the OPP so that the media get overwriten before your disk gets full.
Also, you should not use append when you are writing to 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.
