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Veritas NetBackup™ Administrator's Guide, Volume I

Last Published: 2017-09-25

Product(s): NetBackup (8.1)

About assigning retention periods

The retention period for data depends on the likelihood of restoring information from media after a certain period of time. Some types of data (financial records, for example) have legal requirements that determine the retention level. Other data (preliminary documents, for example) can probably be expired when the final version is complete.

A backup's retention also depends on what needs to be recovered from the backup. For example, if day-to-day changes are critical, keep all the incremental backups in addition to the full backups for as long as the data is needed. If incremental backups only track work in progress toward monthly reports, expire the incremental backups sooner. Rely on the full backups for long-term recovery.

Establish some guidelines that apply to most of the data to determine retention periods. Note the files or the directories that have retention requirements outside of these guidelines. Plan to create separate policies for the data that falls outside of the retention requirement guidelines. For example, place the files and directories with longer retention requirements in a separate policy. Schedule longer retention times for the separate policies without keeping all policies for the longer retention period.

The following table describes recommended retention periods for different types of backups.

Table: Recommended retention periods for different types of backups

Type of backup	Description
Full Backup	Specify a time period that is longer than the frequency setting for the schedule. (The frequency is how often the backup runs). For example, if the frequency is one week, specify a retention period of 2-4 weeks. Two to 4 weeks provides enough of a margin to ensure that the current full backup does not expire before the next full backup occurs.
Differential Incremental Backup	Specify a time period that is longer than the period between full backups. For example, if full backups occur weekly, save the incremental backups for 2 weeks.
Cumulative Incremental Backup	Specify a time period that is longer than the frequency setting for the schedule. (The frequency is how often the backup runs). For example, if the frequency setting is one day, specify a retention period of one week. One week provides enough of a margin to ensure that the current cumulative-incremental backup does not expire before the next successful one occurs. A complete restore requires the previous full backup plus the most recent cumulative-incremental backup.

The following table suggests several ways that you can prevent backups from expiring earlier than desired.

Table: Suggestions for preventing prematurely expired backups

Item	Description
Retention period	Assign an adequate retention period. NetBackup does not track backups after the retention period expires. Recovering files is difficult or impossible after the retention period expires. For the backups that must be kept for more than one year, set the retention period to infinite.
Full backups and incremental backups	Assign a longer retention period to full backups than to incremental backups within a policy. A complete restore requires the previous full backup plus all subsequent incremental backups. It may not be possible to restore all the files if the full backup expires before the incremental backups.
Archive schedules	Set the retention period to infinite.
Tape	Set the retention period to infinite. If infinite is unacceptable because of NetBackup database space limitations, set the retention period to match the length of time that the data is to be retained.

Another consideration for data retention is off-site storage of the backup media. Off-site storage protects against the disasters that may occur at the primary site.

Consider the following off-site storage methods as precautions for disaster recovery:

Use the duplication feature to make a second copy for off-site storage.
Send monthly or weekly full backups to an off-site storage facility.
To restore the data, request the media from the facility. To restore a total directory or disk with incremental backups requires the last full backup plus all incremental backups.
Configure an extra set of schedules to create the backups to use as duplicates for off-site storage.

Regardless of the method that is used for off-site storage, ensure that adequate retention periods are configured. Use the NetBackup import feature to retrieve expired backups.

By default, NetBackup stores each backup on a tape volume that contains existing backups at the same retention level. If a backup has a retention level of 2, NetBackup stores it on a tape volume with other backups at retention level 2. When NetBackup encounters a backup with a different retention level, it switches to an appropriate volume. Because tape volumes remain assigned to NetBackup until all the backups on the tape expire, this approach results in more efficient use of media. One small backup with an infinite retention prevents a volume from being reused, even if all other backups on the volume expired.

To mix retention levels on volumes, select Allow multiple retentions per media in the Media host properties.

If you keep only one retention level on each volume, do not use any more retention levels than necessary. Multiple retention levels increase the number of required volumes.

See Media properties.

Note:

Retention levels can be mixed on disk volumes with no restrictions.

More Information

Changing a retention period