R3: Write Durability — fsync-Before-Ack, Survivor Quorum
Ack only what survived: fsync/group-commit durability barrier, survivor quorum, and read-your-writes — the write-side of the P0 stack.
Durability
R2: Degraded-Read Survivor Fallback and Self-Heal
When a local replica is corrupted or missing, degraded read fetches from healthy survivors transparently, while a background rebuild loop restores cluster redundancy.
R1: Failure-Domain-Aware Placement
Replicas must not ride in the same rack: CRUSH weights become rack/zone/DC-aware so a single domain failure can’t lose the data.