Data is redundantly replicated between TiKV nodes using the Raft Consensus Algorithm to ensure recoverability should a node failure occur. Only when the data has been written into more than 50% of the replicas will the application return ACK (two out of three nodes). However, theoretically, two nodes might crash. Therefore, except for scenarios with less strict requirement on data safety but extreme requirement on performance, it is strongly recommended that you enable the sync-log mode.
As an alternative to using sync-log, you may also consider having five replicas instead of three in your Raft group. This would allow for the failure of two replicas, while still providing data safety.
For a standalone TiKV node, it is still recommended to enable the sync-log mode. Otherwise, the last write might be lost in case of a node failure.