How do retention settings work?
Customizing backup retention lets you specify the length of time recovery points are kept on the device before being automatically purged.
Tiered retention versus basic retention
Traditional (basic) retention settings perform a simple removal of snapshots older than a certain number of days. All snapshots younger than the specified cutoff date are retained. Over time, these basic retention settings tend to waste storage capacity and also lead to performance penalties.
Tiered retention settings are an efficient method involving granular recovery points for recent time frames with fewer recovery points retained for older backups. Think of tiered retention as a series of passes. Each pass "marks" a given snapshot to be retained. A snapshot that is "marked" by any pass must be retained. Tiered retention settings allow you to specify the number of daily, weekly, monthly, and even yearly recovery points for a given protected system, with intervening backups automatically removed and consolidated.
Questions on basic settings? See How to change the backup retention settings of a protected system.
There are three types of passes available:
Pass to retain all snapshots
You can set this to retain a specific number of days. This must be a positive, non-zero number. If you select an invalid value, the default will automatically set to 14 days. The retention period is relative to the date/time of the newest snapshot, or the current date/time, whichever is older. All snapshots newer than the retain-all-oldest-mark-date will be marked for retention.Tab content
Pass to retain a certain number of snapshots
There are four instances of this type of pass:
- End of day
- End of week
- End of month
- End of year
These passes are all independent of each other. In other words, the "time periods" for each of these overlap. They are all relative to the "retain-all-oldest-mark-date" and the times for each are not relative to each other.
In this way, each pass simply marks additional recovery points that need to be retained, changing the configuration of a different "end of period" pass does not change another "end of period" pass.
Airgap is deployed by default to ensure recoverability of recent backups. Fro more information on AirGap, please review this article
Q: What happens during the retention passes if there have been no backups today?
A: The retention time window starts yesterday. Essentially, if backups stop occurring, retention cleanup will stop occurring.
Q: If a system clock is improperly set to the future, and then a snapshot is created, what happens when the clock is set backwards to the correct date/time?
A: The "retain-all-starting-date" is either the date/time of the newest snapshot, or the current date/time, whichever is older. (This ensures that a "parked" system will not start "losing" snapshots.)
Q: Are ALL snapshots newer than the "retain-oldest-mark-date" marked for retention?
Q: If I specify a value < 0 for my "effective-number-of-periods" setting, what will happen?
A: Your "effective-number-of-periods" settings will default to unlimited.
Q: What happens if I disable the "effective-number-of-periods" by setting it to zero?
A: The pass will be skipped without doing anything. No end of period snapshots for that type of period will be marked for retention.
Q: How is the oldest snapshot for a day interval determined?
A: The latest snapshot is chosen from all snapshots included in the date interval between 00:00 and 23:59 of the day of the year determined by the date parameters according to the date data type.
- For example: To determine the last snapshot of the daily period, we select all snapshots that relate to the time between 2021-04-28 00:00:00, 2021-04-28 23:59:59. The oldest snapshot will be the one that is closer to the end time of the current day period.
Q: How do I determine the oldest snapshot for a week?
A: The oldest snapshot for a week interval is determined by selecting the latest snapshot for all snapshots included in the date range between 00:00 on the first day of the week and 23:59 on the last day of the week, as defined by the date parameter set according to the Python date data type "isocalendar" function.
Q: When a protected system is configured for replication, are snapshots deleted that have not yet been successfully transferred to all configured vaults and ingested into ZFS?
A: No, snapshots that have not yet been successfully transferred to all configured vaults and ingested into ZFS cannot be deleted and will not be removed by retention cleanup regardless of what settings the user has chosen for retention.
Q: Do retention policies vary based on the license type?
A: Protected systems licensed on an appliance using Storage Licensing have a fixed mandatory retention policy on Axcient-hosted vaults. (The actual policy is dependent on the Storage License selected (3-year or 10-year), with changes to retention settings on the vault locked out. Appliance retention settings may be selected at will.)
Q: Are there any situations were retention cleanup on vaults is blocked?
A: Retention cleanup on vaults is blocked for a protected system while network recovery back to an appliance is in progress. While the job is active, retention cleanup will not occur and snapshots will not be removed.
Q: How efficient is the retention cleanup algorithm?
A: The retention cleanup algorithm should use a reasonable amount of memory (< 1 GB) and take a reasonable amount of time (< 5 seconds) even for a protected system that has 10,000 snapshots.
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