Backup retention controls how long recovery points will be retained on the device before being automatically purged.
There are two modes of backup retention: Basic and Tiered.
- Basic Retention mode retains all snapshots for the specified number of days.
- Snapshots older than the selected time window are removed from the system.
- Tiered Retention mode retains all snapshots for a set number of days similar to Basic mode. Thereafter it retains a set number of daily, weekly, monthly, and yearly snapshots.
- The system will keep the LAST available snapshot for each period of time. (For example, the last snapshot of the day, week, month, or year).
- The value for Retain All Snapshots must be greater than 0 (Zero)
- Setting any retention period value (daily, weekly, monthly, yearly) to -1 indicates Keep Forever for that interval.
The default settings are presented in the image below:
All snapshots will be retained for 14 days.
After 14 days, we begin keeping the last snapshot of the day for 30 days, the last snapshot of the week for 10 weeks, and the last snapshot of the month for 6 months. Yearly snapshots will not be retained.
Daily, weekly, monthly, and yearly retention are all calculated based on the end of the Keep All period and may overlap with one another. Overlapping snapshots are not deleted until they are no longer valid for any retention Interval. (For example, the last snapshot of the day on December 31 is both a monthly and a yearly and will not be deleted until it is beyond both the monthly and yearly retention intervals.)
- For example, suppose that it is 1:00 p.m. on January 18th. In this case, we would have all snapshots taken from 12:00 a.m. on January 4th up to the present time (Keep all for 14 days).
- The last snapshot of each day taken on December 4th through January 3rd (Keep 30 Daily's).
- Our most recent weekly would be the last snapshot of the day taken on the most recent Sunday, say, December 28th.
- We would also have additional weekly snapshots from the previous 9 Sunday’s (assuming backups are taken on Sunday. Weekly backups are chosen based on the last backup taken within a calendar week, starting 12:00 a.m. Monday through 11:59 p.m. Sunday)
- Our monthly snapshots would be the last snapshot of the day taken during the preceding 6 months. For example, on December 31, November 30, October 31, and so on. Again note that the snapshot preserved will be the LAST snapshot that exists from the given month.
- Finally, our yearly snapshots would be the last snapshot of the day taken on the PREVIOUS year. For example: December 31st or last year, etc. It is critical to note that specifying 1 or more yearly backups does NOT, in itself, guarantee that you will have a year of backup retention for the protected system. For example, if today is January 1st, the snapshot retained to satisfy 1 yearly backup is the last backup from YESTERDAY, December 31st.
Note that ALL of the intervals (daily, weekly, monthly, yearly) calculated begin on the day after the keep-all-snapshots date. For example, if you elect to keep 14 daily snapshots, two of those snapshots will overlap with the first two weekly snapshots, etc.
If no snapshot exists for any of the given days listed above, the next most recent snapshot within the time interval will be chosen. For example, if no snapshots exist on Saturday or Sunday, the last snapshot taken on Friday will be selected for the weekly, and so on.