NAME

       votequorum_overview - Votequorum Library Overview

OVERVIEW

       The  votequorum  library  is  delivered  with  the  corosync  project.  It is the external
       interface to the vote-based quorum service. This service is  optionally  loaded  into  all
       nodes  in  a  corosync  cluster  to avoid split-brain situations. It does this by having a
       number of votes assigned to each system in the cluster  and  ensuring  that  only  when  a
       majority of the votes are present, cluster operations are allowed to proceed.

       The library provides a mechanism to:

       * Query the quorum status

       * Get a list of nodes known to the quorum service

       * Receive notifications of quorum state changes

       * Change the number of votes assigned to a node

       * Change the number of expected votes for a cluster to be quorate

       *  Connect  an  additional  quorum device to allow small clusters to remain quorate during
       node outages.

VIRTUAL SYNCHRONY

       Votequorum is the only one service where communication  with  library  is  allowed  during
       synchronization  phase.  This  makes  it possible for quorum device to react to membership
       change and decide to vote or  not  without  timing  hazard,  because  corosync  stands  in
       synchronization phase until qdevice on all nodes votes or timeout expires.

       As  a  side  effect, extended virtual synchrony is broken for the votequorum service. This
       means, that messages sent during  synchronization  phase  can  be  delivered  sooner  then
       messages sent right before sync phase began. This applies also for local messages.

BUGS

       No known bugs at the time of writing. The authors are from outerspace. Deal with it.

SEE ALSO

       corosync-quorumtool(8),  votequorum(5),  votequorum_initialize(3), votequorum_finalize(3),
       votequorum_getinfo(3),         votequorum_trackstart(3),          votequorum_trackstop(3),
       votequorum_fd_get(3),          votequorum_dispatch(3),          votequorum_context_set(3),
       votequorum_context_get(3), votequorum_setexpected(3), votequorum_setvotes(3)