Having a bookkeeper replicaCount at 4, what would be a most natural Ensemble-Qw-Qa setting, if I want to tolerate one of the replicas going down even for a considerable amount of time (node outage, etc.). I believe E should be less than replicaCount (to tolerate one replica going down), while best to have E=Qw (avoid issues with lack of consistency). So I guess 3-3-3 or 3-3-2 would be best. What configurations would be recommended?

We recommend 2-2-2

I guess it's the reverse, 2-2-2 can tolerate 2 data copy lost?

For Apache BookKeeper, the most common and recommended quorum configuration for balancing latency, durability, and availability is typically

E=3, Qw=3, Qa=2

. This configuration provides a good balance between durability and latency. Every entry is replicated to all three bookies in the ensemble. This maximizes durability, ensuring each entry has a full set of replicas. The client waits for an acknowledgment from only a majority of bookies (two out of three). This lowers write latency by not waiting for the slowest bookie. Furthermore, the system can tolerate the failure of

Qa - 1

bookies without any data loss.

2-2-2 means write two copies, and make sure the 2 copies are written to two bookies before acknowledging to the producer. You only write 2 data copies, and can only tolerate 1 data copy lost

Thanks for all the responses!