The only obstacle they mention to realizing 5-10µs latency per se is that networking infrastructure can't yet support it. The paper also talks about other issu

The only obstacle they mention to realizing 5-10µs latency per se is that networking infrastructure can't yet support it. The paper also talks about other issues that will need to be resolved (Section 4.1): software overheads like context switching and polling network devices, and protocol issues (e.g. TCP's minimum retransmission timeout is currently 200 milliseconds, which would make even a single dropped packet catastrophic for latency). I do agree that it is a bit suspect for the authors to go advocate at length for low-latency RPCs, but not volunteer to step up to the plate to do the innovation in switches and network hardware that this will require. What specifically are the common strategies for backup to disk? Well, most schemes follow some variant of write-ahead logging to a "stable" location: either local disk or to the RAM of a remote network node (and then assuming that the local and remote nodes won't fail simultaneously).