

Have you considered a distributed filesystem such as GlusterFS or DRBD? I believe those support synchronous replication so writes will go to all the configured machines before acknowledging the write. Performance will likely take a hit the greater the number of clusters in the cluster.
My take on the scoring
Very Easy: Multiple easy install methods (e.g., one-command OS package, single binary, and/or Docker). If only one install method it should be single binary or OS package. Great documentation. 18–20 points
Easy: Limited easy methods or only one. Some configuration may be needed, good documentation. 15–17 points
Moderate: Docker is the only method or manual setup. Average to pool documentation 11–14 points
Hard: Complex setup, needs regular updates or custom config (e.g. DNS, spam) 6–12 points
Very Hard or Proprietary: Little to no self-hosting support, undocumented 0–5 points