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From Yonik Seeley <yo...@lucidworks.com>
Subject Re: Minimum HA Setup with SolrCloud
Date Thu, 06 Dec 2012 22:28:43 GMT
On Thu, Dec 6, 2012 at 5:21 PM, Jack Krupansky <jack@basetechnology.com> wrote:
> If 1 is the minimum, what is the 3 "minimum" all about?

The minimum for running an ensemble (a cluster) and having any sort of
fault tolerance?

> The zk web page does say "Three ZooKeeper servers is the minimum recommended
> size for an ensemble, and we also recommend that they run on separate
> machines" - but it does say "recommended".
>
> But back to the original question - it sounds as if 4 nodes would the
> recommended minimum number of nodes if you want to tolerate one machine
> going down and maintaining that 3 zookeeper recommended minimum ensemble.

Nope - the "ensemble" are not the number of servers that are currently
up, but the number in the cluster.  This is important to prevent split
brain.
3 ZK servers means that a majority of the servers is 2, hence you can lose 1.
5 ZK servers means that a majority of the servers is 3, hence you can lose 2.

-Yonik
http://lucidworks.com

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