Replicas in one rack vs in different racks
Two replicas in one rack fail together when the rack switch fails. Replicas in different racks fail apart. Three replicas serve 80,000 lookups/s, and the load needs two. With two in rack 2, p99 is 568 ms and 9.5 percent of requests fail. With one in each rack, p99 is 25 ms and 0.5 percent fail.
Two rows · 3 of 3 replicas up · load served
Quorum 2 of 3 · commit 9.0 ms
Case 1
Three replicas serve 80,000 lookups/s, and the load needs two. The rack 2 switch fails at 0:20 for 15 s. Power feed A fails at 0:40 for 15 s. p99 must stay below 50 ms and errors below 1 percent.
| Measure | Goal | Two replicas in rack 2 | One replica in each rack |
|---|---|---|---|
| p99 latency | under 50 ms | 568 ms Fail | 25 ms Pass |
| Error rate | under 1% | 9.5% Fail | 0.5% Pass |
| Monthly cost | 229 USD/mo | 229 USD/mo | |
| Error rate | 9.5% | 0.5% |