Snapshots

Snapshots recommendations save money by deleting old and extraneous snapshots. 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.

Examples

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.

Scope

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.

Deletion savings for a snapshot are calculated as: unique_blocks * block_size / 1,073,741,824 (bytes per GB) * price_per_unit ($/GB-month).

If you delete all of the snapshots for a particular volume, then you may end up saving more than the sum of the individual snapshot recommendations.

Recommendation Reasons

Snapshots are evaluated in the following priority order:

  1. In Use In Image — The snapshot is referenced by an AMI. No deletion is recommended.
  2. Cloudrec Backup — The snapshot was created by Cloud Optimizer as a backup (e.g., before deleting a volume). These are kept within policy thresholds. No deletion is recommended.
  3. Cloudrec Backup Too Old — The snapshot was created by Cloud Optimizer as a backup, but it is older than the retention policy allows. Deletion is recommended.
  4. No Volume Found — The source volume no longer exists. Deletion is recommended. These orphaned snapshots are grouped together for easy review.
  5. Volume Not Attached — The source volume is not attached to any instance. Deletion is recommended.
  6. Volume Attached To Non-Running Instance — The source volume is attached to a stopped instance. Deletion is recommended.
  7. Too Many Snapshots — The volume has more snapshots than the retention policy allows for the snapshot’s age range. The oldest excess snapshots are recommended for deletion. Snapshots older than 365 days are always flagged under this reason, since no retention is configured beyond that age.
  8. Valid Snapshot — The volume is actively used and the snapshot is within policy limits. No action needed.

How we find the best savings

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:

  1. The past 7 days.
  2. The past 7 to 31 days.
  3. The past 31 to 365 days.
  4. Over 365 days ago.

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.

Policies

Snapshots to keep for the first 7 days

Policy key: snapshot:snapshots_for_days_0-7 Default: 7

This is the number of snapshots to keep within the past 7 days. The default of 7 corresponds to one snapshot per day.

Snapshots to keep for the first month (excluding the first week)

Policy key: snapshot:snapshots_for_days_7-31 Default: 4

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.

Snapshots to keep for the first year (excluding the first month)

Policy key: snapshot:snapshots_for_days_31-365 Default: 11

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.

Snapshots to keep after the first year

Default: 0

There is no configurable policy for snapshots older than 365 days. All snapshots beyond this age are recommended for deletion under the “Too Many Snapshots” reason.