None of this. It's in the blog post in a lot of detail =) The 5ms write latency is because the backend distributed block storage layer is doing synchronous re

None of this. It's in the blog post in a lot of detail =) The 5ms write latency is because the backend distributed block storage layer is doing synchronous replication to multiple servers for high availability and durability before ack'ing a write. (And this path has not yet been super-performance-optimized for latency, to be honest.)