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From "Doug Meil (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-5397) [book] zookeeper quorum mistake
Date Tue, 14 Feb 2012 18:54:00 GMT

    [ https://issues.apache.org/jira/browse/HBASE-5397?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13207904#comment-13207904
] 

Doug Meil commented on HBASE-5397:
----------------------------------

yep
                
> [book] zookeeper quorum mistake
> -------------------------------
>
>                 Key: HBASE-5397
>                 URL: https://issues.apache.org/jira/browse/HBASE-5397
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Andre Medeiros
>            Assignee: Doug Meil
>            Priority: Minor
>
> In Chapter 2, section 2.5 "ZooKeeper" under "How many ZooKeepers should I run?" there
is the sentence
> *There can be no quorum if the number of members is an even number.*
> This is not true. In ZooKeeper, an even number of peers is supported, but it is normally
not used because an even sized ensemble requires, proportionally, more peers to form a quorum
than an odd sized ensemble requires. For example, an ensemble with 4 peers requires 3 to form
a quorum, while an ensemble with 5 also requires 3 to form a quorum. Thus, an ensemble of
5 allows 2 peers to fail, and thus is more fault tolerant than the ensemble of 4, which allows
only 1 down peer.

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