Redisの2.8.2からsplit brainの対策がされているようです

2.8.2 [FIX] Sentinel better desynchronization to avoid split-brain elections https://github.com/antirez/redis/blob/2.8/00-RELEASENOTES#L149

Sentinel: better time desynchronization. https://github.com/antirez/redis/commit/75347ada7f431925b97b037b56b5e3801e3fd16d

Sentinels are now desynchronized in a better way changing the time handler frequency between 10 and 20 HZ. This way on average a desynchronization of 25 milliesconds is produced that should be larger enough compared to network latency, avoiding most split-brain condition during the vote.

Now that the clocks are desynchronized, to have larger random delays when performing operations can be easily achieved in the following way. Take as example the function that starts the failover, that is called with a frequency between 10 and 20 HZ and will start the failover every time there are the conditions. By just adding as an additional condition something like rand()%4 == 0, we can amplify the desynchronization between Sentinel instances easily.

こちらからは以上です。