About media overwrite protection and append periods

Article:HOWTO73312  |  Created: 2012-03-02  |  Updated: 2012-03-16  |  Article URL http://www.symantec.com/docs/HOWTO73312
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About media overwrite protection and append periods

Each media is associated with a media set, which is a set of rules that manage media.

These rules include overwrite protection and append periods.

Table: Overwrite protection and append periods

Rule

Description

Append period

The amount of time that data can be appended to media. It is measured from the time the media was first allocated. It can be specified in hours, days, weeks, or years.

Overwrite protection period

The amount of time that media is protected from being overwritten. The period is measured from the time of the last write to the media, that is, at the end of the last append or overwrite job. It can be specified in hours, days, weeks, or years. When the overwrite protection period is over, the media becomes recyclable and can be overwritten.

The overwrite protection period begins when the backup job is completed. If there is an append period, the overwrite protection period begins again each time an append job completes. Because the overwrite protection period does not begin until the job completes, the amount of time that is required to complete the job takes affects when the media can be overwritten. You may shorten the overwrite protection period to take into account the amount of time a job may run.

For example, you set the overwrite protection period for seven days. You also set the append period for four days to ensure that data is not overwritten for at least seven days. The data can be appended to the media for the next four days. The last data that is appended to this media is retained for at least seven days.

Note:

Any media can be overwritten if the overwrite protection level is set to None.

See About media overwrite protection levels for tape and disk cartridge media

Your media rotation strategy must balance between the need to save data as long as possible, and the fact that media are not in infinite supply. The media set rules allow Backup Exec to identify which media can be written to and which media are overwrite-protected. You should consider the use of disk storage for backup data.

See About disk storage.

The following graphic shows the relationship between the append period and the overwrite protection period.

Figure: Append periods and overwrite protection periods

Append periods and overwrite protection periods

The append and overwrite protection periods that you specify apply to all the data on the media.

Each time data is written to a media, the time remaining in the overwrite protection period is reset, and the countdown is restarted.

Figure: How overwrite protection periods are reset

How overwrite protection periods are reset

The amount of time that is required to complete the job takes affects when the media can be overwritten.

For example, suppose that you create a media set named Weekly with an overwrite protection period of seven days. You also specify an append period of zero days, and you schedule a full backup job to run each Friday at 20:00. When it is time for the full backup to run at 20:00 the following Friday, the job cannot run. The first backup job that ran the previous Friday did not complete until 21:10. The overwrite protection period for the Weekly media set still has 70 minutes remaining.

To prevent this situation, you can shorten the overwrite protection period to account for the amount of time a job may run. For this example, the scheduled job recurring at 20:00 can run if the overwrite protection period is set to six days instead of seven days.


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