basically if it does not use synchronous replication. and master server switch then 2 client could think they own an unexpired lock. But if it does synchronous

basically if it does not use synchronous replication. and master server switch then 2 client could think they own an unexpired lock. But if it does synchronous replication without using a consensus algorithm like Paxos or Raft then the system become unwrittable if an instance go down.