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MariaDB 10.1 packages do not contain (yet) MariaDB Galera Cluster libraries. This library is developed by another company. After you have installed MariaDB 10.1 you need to install Galera Cluster library separately and then configure MariaDB 10.1 server to use this library and set up the configuration.
@janlindstrom I'm sorry but you are wrong.
"In MariaDB 10.1 the MariaDB Server and MariaDB Galera Server packages have been combined and Galera packages and their dependencies get installed automatically when installing MariaDB. The Galera parts remain dormant until configured, like a plugin or storage engine." - https://mariadb.com/kb/en/mariadb/getting-started-with-mariadb-galera-cluster/