Snapshots can be an effective backup strategy, but their ease of use also makes them easy to forget about.
You are charged by the number of unique blocks among all of your “related” snapshots. Snapshots are “related” if they are snapshots of the same volume.
Note that AWS treats fully empty blocks as not existing for the purposes of cost.
If you create a snapshot of a 0-block volume, this snapshot will cost you nothing, since there are no blocks at all in the snapshot.
If you create a snapshot of a 1,000-block volume, you will be charged for 1,000 unique snapshot blocks. However, if you create another snapshot of the same volume without changing any data, then you will still be charged for 1,000 unique snapshot blocks. If you then make a small change (say 1 block’s worth) and take a third snapshot, then you will be charged for 1,001 unique snapshot blocks.
Because snapshots are billed by the number of unique blocks, there is really no good way to view the cost of any given snapshot.
We show the savings of deleting any given snapshot by computing the cost of deleting that snapshot. All of its unique blocks are removed, and all of the non-unique blocks are still present in at least one other snapshot.
If you delete all of the snapshots for a particular volume, then you may end up saving more than the sum of the the individual snapshot recommendations.
We generally assume that you want more recent snapshots and fewer older snapshots.
We break up the time into four periods, and we recommend that you keep a certain number of snapshots within each of those periods:
We then recommend that you delete the oldest snapshots in each of those periods that exceed the desired number.
Note that snapshots that are used in images will not be subject to deletion recommendations.
Note also that snapshots that were created as part of another recommendation (such as deleting a volume) will be kept for 1 year and will then be recommended to be deleted.
This is the number of snapshots to keep within the past 7 days. The default of 7 corresponds to one snapshot per day.
This is the number of snapshots to keep within the past 31 days, excluding the past 7. The default of 4 corresponds to one snapshot per week.
This is the number of snapshots to keep within the past 365 days, excluding the past month. The default of 11 corresponds to one snapshot per month.
This is the number of snapshots to keep after the past 356 days. The default of 0 corresponds to keeping no snapshots over 1-year old.