Backup Retention – Part 3 of 3
Incremental Method
This method has a few names and is fairly simple to implement. It involves determining how long you wish to maintain a copy of your data and how many tapes you wish to use. It is based on labeling each backup with a number and then incrementing them through adding and retaining one Backup Set each week. It can be configured to allow for either 5-or-7 day backup schemes. An incremental tape rotation method is set up as follows for a 5 day backup scheme.
The above example assumes 9 backups are being kept. At any point in time you would be able to have direct access to the backups for the last 5 days, then the Monday backup for the last 5 weeks. At week 6 you would be overwriting the oldest backup.
The total disk space requirements assuming a 200gb daily backup would be 1800gb (1.8tb). To extend this out to 4 months, or 12 weeks it would take 16 backups for a total disk space of 3.2tb.
Round Robin
Round Robin uses a single backup set for each day of the workweek. This ensures that you will never lose more than a day’s worth of data, but it keeps only a week’s worth of your information.
Combined Methods
Another alternative is to use one backup method for the daily process, and another for the weekly process.
Round Robin and Abacaba / Tower of Hanoi
For instance if you were to use the Round Robin for the daily backup, followed by the Abacaba – Tower of Hanoi for the weekly backup, you would end up using 1tb for the weekly backup, then 1.4tb for the weekly backups, for a total of 2.4 tb to retain backups for 64 weeks (1.24 years).
The total disk requirement for this backup scheme assuming 200gb daily backups is 1000gb (1tb).
Comparisons
The following chart outlines the comparisons between the different basic backup rotation methods.
| Method | Disk Usage | Retention Time |
| Grandfather, Father, Son – GFS (1) | 2200gb (2.2tb) | 4 months |
| Grandfather, Father, Son – GFS (1) | 3800gb (3.8tb) | 12 months |
| Abacaba – Tower of Hanoi (1) | 1400gb (1.4tb) | 2 months |
| Abacaba – Tower of Hanoi (2) | 1600gb (1.6tb) | 8 months |
| Incremental Method (1) | 1800gb (1.8tb) | 6 weeks |
| Incremental Method (2) | 3200gb (3.2tb) | 4 months |
| Round Robin | 1000gb (1tb) | 1 week |
| Round Robin (Daily) + Abacaba / Tower of Hanoi (Weekly) | 2400gb (2.4tb) | 1.24 years |
Summary
Hopefully this will help with the longer term retention that meets your business needs.
If you need help with your backup strategy you can always reach out to Stedman Solutions, LLC and we can help.
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