Servers # = 2F + 1

Protocols using quorums

• 1990 ⇒ Paxos, View-stamped replication
• 2014 ⇒ Raft

Why logs?

1. Maintain order
2. Restransmission
   1. Leader must keep a record of all the log entries.
3. Persistence
4. Space for tentative operations

Logs are identical on all servers