While I'm a huge fan of Docker I will maintain that CoreOS is not ready for production in most capacities and recommend against using it in its current form.
CephFS had a similar-ish problem, where if you happened to ever own less than 3 nodes (almost always because of the above), it would have a real problem self-healing and start to get confused and re-elect bad nodes to quorum leadership, possibly clobbering all your registry data. We contributed a patch back to Deis to use S3 as a registry persistence layer because, well, having a volatile registry sucked. We were about to develop a control layer for quorum services to live on separate of the application services we were developing, and using a proxy in the quorum layer to communicate stuff like etcd. I would highly recommend this approach if you end up with any services that require a quorum.
I would prefer to avoid many disk operations in the first place. Not sure, if it's applies to your problem, but have you thought about using something like Sentry (https://getsentry.com/ || https://github.com/getsentry/sentry)? Maybe there is some other tool that could help you here, I'm often impressed by the Open Source community and the vast number of different packages for (almost ;)) every technological problem.