Cloud cost
Incremental snapshot
A backup that stores only the blocks changed since the previous snapshot, not a full copy. Deleting one frees far less space than its listed size suggests.
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Definition
After the first one, block-storage snapshots are incremental. This applies to EBS and to the equivalent at most providers. Each new snapshot points to the unchanged blocks in earlier snapshots instead of copying them. That makes frequent snapshots cheap in principle. It also means the console's per-snapshot size overstates what deleting one snapshot would free. That size is the full logical size of the volume at that point.
Automated backup schedules with no retention policy are the usual way this becomes real money. The low cost of each incremental snapshot does not stop them piling up. They pile up for as long as nothing expires them.
Where it shows up
In the console, an incremental snapshot's size appears as the full logical size of the volume at that point in time. It does not show the incremental bytes the snapshot stores. EBS lists each snapshot in a chain this way. So the number on screen does not match the space you free by deleting the snapshot.
What makes it expensive
An automated backup schedule with no retention policy is the usual cause. Each new snapshot costs so little that the growing total goes unnoticed for a long time. Watch the snapshot count. If it climbs month after month and no expiry rule exists in the schedule, the chain has no end. It will not grow one by itself.
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