[nojvek]

Obviously depends on how they delivered read after write.

Likely they don't have to physically move data of objects, but the layer that writes and reads coordinates based on some version control guarantees e.g in database land MVCC is a prominent paradigm. They'd need a distributed transactional kv store that tells every reader what the latest version of the object is and where to read from.

An object write only acknowledges finished if the data is written and kv store is updated with new version.

They could do this bucket by bucket in parallel since buckets are isolated from each other.