[jira] [Updated] (HBASE-5397) [book] zookeeper quorum mistake

["Doug Meil (Updated) (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HBASE-5397?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Doug Meil updated HBASE-5397:
-----------------------------

    Attachment: docbkx_hbase_5397.patch
    
> [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
>         Attachments: docbkx_hbase_5397.patch
>
>
> 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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