[twistedpair]

Not sure about your usage model, but if you have a defined retention for customer data (e.g. 1 year), then you can start pushing new data to a different tier/cloud provider, as the old data drops off, and a year later, you're completely "migrated", without having to stage a stop the world migration between services.

[zmmmmm]

In our case, it's effectively "forever" storage. Which is to say, we are obliged to retain data for at least 10 years but targeting 20 years.

At this point we are doing this with on-premise tape backup but that is in part because I'm yet to be convinced that we can trust cloud providers with this, especially since our future retrieval needs are unclear (some outlier scenarios could see us needing to retrieve substantial fractions of the data). Not to mention that even the coldest cloud storage seems to still be substantially more expensive than DIY tape archival (admittedly, not taking into account things like internal IT staff costs etc).