NetBackup retention is set up on a time or date basis, meaning that you specify a number of days, a period of time, or exact days that the dataset image is active. The dataset images have no awareness of how many copies are in retention.
While it is strongly recommended that your backup strategy be designed or revised to use the calendar or time-interval retention provided by NetBackup, it is possible to implement a generation-based retention schema using scripts that perform the following:
- Set all retentions on desired generation-capable images to Infinite. This will allow any time span to be possible between generations. Set the retention to Infinite within the NetBackup policies used for the TARA streams.
- Use the Keyword feature in the policies to group the images together for a complete generation. An incrementing value can be used such as "G1…G2…G3" and so on. The higher the number, the more recent the generation.
- Implement scripting to manage images by the Keyword. The script will list images by using the bpimage command and build a condensed generation list using the Keyword value. For example, the desired generation number is 4 and after today's successful backup, the current generation list is G5, G6, G7, G8, and G9. The images with the Keyword value of G5 are then expired by the bpexpdate command in your script.