My understanding (which is admittedly limited): There are 2 nodes left out of 3, so when both machines respond they will get 2/3 of the vote, thus forming a majority. If you only had 2 machines in your cluster for example, then if 1 died, then the others vote would only make up 1/2 of the vote, which is not the majority, so you get no extra redundancy in having 2 machines over having 1.
On Thu, Jan 16, 2014 at 3:59 PM, Otis Gospodnetic < [email protected]> wrote: > Hi, > > Somebody asked me recently and I "got stuck" trying to explain this. > When people ask how many ZK nodes they should have a common answer is "odd > number: 3 or 5 or ...", so ZK can do majority voting. Correct so far? > Another reason is for HA - if one ZK node dies, there are still 2 of them > left. And this is where I am missing something core - with just 2 nodes > left, how can ZK do majority voting now? > > Thanks, > Otis > -- > Performance Monitoring * Log Analytics * Search Analytics > Solr & Elasticsearch Support * http://sematext.com/ >
