1VOTEQUORUM_OVERVIEWC(o3r)osync Cluster Engine Programmer's MaVnOuTaElQUORUM_OVERVIEW(3)
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6 votequorum_overview - Votequorum Library Overview
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9 The votequorum library is delivered with the corosync project. It is
10 the external interface to the vote-based quorum service. This service
11 is optionally loaded into all nodes in a corosync cluster to avoid
12 split-brain situations. It does this by having a number of votes
13 assigned to each system in the cluster and ensuring that only when a
14 majority of the votes are present, cluster operations are allowed to
15 proceed.
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17 The library provides a mechanism to:
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19 * Query the quorum status
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21 * Get a list of nodes known to the quorum service
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23 * Receive notifications of quorum state changes
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25 * Change the number of votes assigned to a node
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27 * Change the number of expected votes for a cluster to be quorate
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29 * Connect an additional quorum device to allow small clusters to remain
30 quorate during node outages.
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33 Votequorum is the only one service where communication with library is
34 allowed during synchronization phase. This makes it possible for quorum
35 device to react to membership change and decide to vote or not without
36 timing hazard, because corosync stands in synchronization phase until
37 qdevice on all nodes votes or timeout expires.
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39 As a side effect, extended virtual synchrony is broken for the votequo‐
40 rum service. This means, that messages sent during synchronization
41 phase can be delivered sooner then messages sent right before sync
42 phase began. This applies also for local messages.
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45 No known bugs at the time of writing. The authors are from outerspace.
46 Deal with it.
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49 corosync-quorumtool(8), votequorum(5), votequorum_initialize(3), vote‐
50 quorum_finalize(3), votequorum_getinfo(3), votequorum_trackstart(3),
51 votequorum_trackstop(3), votequorum_fd_get(3), votequorum_dispatch(3),
52 votequorum_context_set(3), votequorum_context_get(3), votequorum_setex‐
53 pected(3), votequorum_setvotes(3)
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55corosync Man Page 2012-01-12 VOTEQUORUM_OVERVIEW(3)