_BackupSetVolumesNote

A Backup Set allows to retain an isolated use case oriented set of the last at most N snapshots of one or more EBS volumes.

When the EBS Volume task's Grow & Prune Snapshot Backup Set action executes, it will:

1. Create a new EBS snapshot for each selected EBS volume and tag the snapshot with a key Backup Policy and a value based on the Backup Set name (thus "grow the snapshot backup set")
2. Enumerate all existing snapshots for the selected EBS volume(s) that are tagged with a key Backup Policy whose value matches matches the Backup Set name
3. If it finds more snapshots in this Backup Set than defined by the Backup Retention number, it will delete the oldest snapshots in FIFO order until only the desired number is left (thus "prune the snapshot backup set")

While there are also separate Grow Volume Backup Set and Prune Volume Backup Set actions to separate the two activities (for example, to only grow the backup set on each work day, but prune it to the last work day's image at the end of the week), the Grow & Prune Volume Backup Set action covers most rotating backup use cases in a single operation.