Trying to understand retention policies

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After each snapshot is taken, kopia will assign retention tag to snapshots and delete snapshots that don’t have any assigned tag.

Tags are assigned as follows:

  • latest-N will be assigned to all snapshots going backwards where the most recent snapshot gets latest-1, previous is latest-2 and so on.

  • hourly-N will be assigned to the latest snapshot within each respective hour, going back no more than M hours where M is defined by --keep-hourly parameter.

For example if you have done snapshots at:

2001-01-01 14:01 - not hourly because 14:30 was the last snapshot of this hour
2001-01-01 14:30 - hourly-2
2001-01-01 15:01 - not hourly because 15:55 was the last snapshot of this hour
2001-01-01 15:02 - not hourly because 15:55 was the last snapshot of this hour
2001-01-01 15:40 - not hourly because 15:55 was the last snapshot of this hour
2001-01-01 15:50 - not hourly because 15:55 was the last snapshot of this hour
2001-01-01 15:55 - hourly-1

Similarly daily-N is assigned to the latest snapshot within each day:

2001-01-01 14:01 - not daily because 15:55 was done the same day
2001-01-01 15:55 - daily-5
2001-01-02 14:01 - daily-4
2001-01-03 15:55 - daily -3
2001-01-04 14:01 - not daily because 15:01 was done the same day
2001-01-04 15:01 - daily-2
2001-01-05 15:55 - daily-1

Same rule applies to weekly, monthly, quarterly and annual retention rules - each of them retains latest snapshot within a given time period up to a defined limit.

Note the limit applies to both count and time, so if you have keep-hourly 48, it will keep no more than 48 hourly snapshots going back no more than 48 hours since the last snapshot.

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