[CherryJimbo]

They're "backups" in the sense of storing customer data, but realistically they're more like instance snapshots for various customer game servers. They're created and restored multiple times a day for every customer as they hop between games (accessed very frequently), so Glacier wouldn't be a good fit.

[hrez]

If it's that much churn, wouldn't it make sense to point new writes/updates to B2 and let s3 naturally drain/lifecycle out its data?

[dgemm]

Probably a technically better solution but it would not make as good of a PR piece as an epic migration.

[amenod]

Actually I think it would sound better - "How to move 23TB without moving (almost) anything". Especially to technical people.