If we use bokbok as a backend access protocol, we can have multiple put! requests inflight. In which case, the techniques in this ticket can be applied to snapshotting as well:

https://www.kitten-technologies.co.uk/project/ugarit/tktview/97b608385736f7f946bc3b3b2a037b0b8945306e

OR we could continue with the original plan, kind of, and make put! fire off a thread (subject to a concurrency limit) to do the actual put, and put any errors returned into an error queue to be returned from the next operation on that storage that returns.