Master/Slave configuration is below. Do you know master/master configuration? 

<datasources>
   <datasource jndi-name="java:jboss/datasources/ExampleDS" pool-name="ExampleDS" enabled="true" use-java-context="true">
   <connection-url>jdbc:h2:mem:test;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE</connection-url>
   <driver>h2</driver>
   <security>
   <user-name>sa</user-name>
   <password>sa</password>
   </security>
   </datasource>
   <datasource jta="true" jndi-name="java:jboss/datasources/RailbaseLabDS" pool-name="RailbaseLabDS" enabled="true" use-java-context="true" use-ccm="true">
   <connection-url>jdbc:mysql://IP1:3306,IP2:3306/DBN?autoreconnect=true</connection-url>
   <driver-class>com.mysql.jdbc.Driver</driver-class>
   <driver>mysql</driver>
   <url-delimiter>|</url-delimiter>
   <security>
   <user-name>DBN</user-name>
   <password>DBN</password>
   </security>
   <validation>
   <valid-connection-checker class-name="org.jboss.jca.adapters.jdbc.extensions.mysql.MySQLValidConnectionChecker"/>
   <check-valid-connection-sql>select 1</check-valid-connection-sql>
   <background-validation>true</background-validation>
   <background-validation-millis>5000</background-validation-millis>
   </validation>
   </datasource>
   <drivers>
   <driver name="h2" module="com.h2database.h2">
   <xa-datasource-class>org.h2.jdbcx.JdbcDataSource</xa-datasource-class>
   </driver>
   <driver name="mysql" module="com.mysql">
   <xa-datasource-class>com.mysql.jdbc.jdbc2.optional.MysqlXADataSource</xa-datasource-class>
   </driver>
   </drivers>
   </datasources>