When is it reasonable to use the Append Period?

When is it reasonable to use the Append Period?

Article: 100025061
Last Published: 2020-10-27
Ratings: 3 1
Product(s): Backup Exec

Problem

Explain in which cases the Append Period should have a value other than zero or infinite.

Error Message

No errors.

Solution

The Append period is the length of time that data may be added to a tape, after an overwrite backup job.  It is very common that users want to utilize all available space on a tape.  However, it is not necessary to use Append periods or append jobs when backup-to-disk folders are targeted. 

Normally, one or more than one tapes are used for the periodic backups in a data protection scheme.

In the most basic scenario, for example, daily full backups are targeted each to one daily tape. These tapes will not be used again, until the retention period is over and the tape should be overwritten.

In our basic example, one tape is used each day. If the retention period is,  let's say, of 15 days, then the media set for the daily tapes will have the following properties:

Media Set Name: Daily Full Backups
Overwrite Protection Period: 15 Days.
Append Period: 0 Days.

If the append period was different than 0, any subsequent backups done during that period, would RESET and EXTEND the Overwrite Protection Period, and the tape would not be available for overwriting on day 16. That day, the backup could be missed, not having any media available for overwriting.

When is it then, convenient to use the Append Period with a value other than zero?

The most reasonable case would be, when the size of the data to be backed up is much smaller and fits several times into the tape capacity.

Going back to our basic daily full backup example, if all the data to be backed up occupied a total of 200 Gb., and the tapes used were LTO4 with a capacity of 800 Gb., it would be a waste to designate one tape for each day. More than one daily backup could fit into one of these media. In our case, Monday's, Tuesday's and Wednesday's backups could all be completed using a single cartridge. (We do 3 days and not 4 just in case data grows somewhat larger than 200 Gb.).

This is the time where the Append Period comes in handy. To be able to do 3 days worth of backups, we would change the media set to these values:

Media Set Name. Daily Full Backups
Overwrite Protection Period: 15 Days.
Append Period: 2 Days.

This new setting for the Append Period, would allow us to complete Tuesday's, and Wednesday's backup on the same tape, which would end up almost full, or at least effectively used.

But now that we have implemented a non-zero value for the Append Period, every time a subsequent backup is completed, the Overwrite Protection Period will be restarted, so the tape will NOT be available for overwrite on day 16. If we target backups to the tape on Tuesday and Wednesday, the tape will be overwrite protected for two more days.

To keep being able to overwrite the tape as planned on day 16, we should change now the Media Set values as follows:

Media Set Name: Daily Full Backups
Overwrite Protection Period: 13 Days.
Append Period: 2 Days.

Backup strategies are usually not as simple as doing one full backup everyday. Protection schemes include incremental and differential jobs during the week, and full backups on weekends and at the end of the month. But if the Append Period's concept is understood correctly, the same method can be used for the daily differentials or incremental, which will obviously occupy much less space than full backups.

The general rule will be, to use a value other than zero for the Append Period, when the data set to be backed up, whether full, differential or incremental, fits two or more times inside the capacity of the target tape.

 

Applies To

Any Backup Exec installation and compatible Windows versions.

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