Small fluctuations in our storage bill
The storage service runs in a dedicated AWS account, so the account bill only reflects the cost of the storage service.
The dominant cost in this account is the Standard-IA bill, but at a glance it can look a little disconcerting. In particular, our Standard-IA bill goes down as well as up – but why would it ever go down? Why would we ever remove objects in Standard-IA? Should we be concerned about the integrity of the storage service?
No – slight fluctuations in the Standard-IA bill are a normal part of storage service operations.
Why?
When objects in the warm replica transition to Glacier, they get removed from Standard-IA. That cost moves from Standard-IA to Glacier.
When objects in the cold replica transition to Glacier Deep Archive, they get removed from Standard-IA. That cost moves from Standard-IA to GDA.
In the graph above, you can see a drop in the Standard-IA bill at the beginning of the month – but it's accompanied by a rise in the Glacier/Deep Archive bill. A bunch of objects just got transitioned into a cheaper storage class.
A substantial drop in the Standard-IA bill may be a red flag, but small fluctuations aren't a cause for concern.
To see this with our real numbers, visit Cost Explorer filtered to storage costs only. Notice how our StandardStorage bill similarly fluctuates (although it's a much smaller part of our bill) – this is when objects transition from Standard to Standard-IA.
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