logback.xml

<configuration>
  <appender name="FILE" class="ch.qos.logback.core.FileAppender">
    <file>/sdcard/testFile.log</file>
    <append>true</append>
    <encoder>
      <pattern>%-4relative [%thread] %-5level %logger{35} - %msg%n</pattern>
    </encoder>
  </appender>

  <appender name="FILE2" class="ch.qos.logback.core.FileAppender">
    <file>/sdcard/testFile2.log</file>
    <append>true</append>
    <encoder>
      <pattern>%-4relative [%thread] %-5level %logger{35} - %msg%n</pattern>
    </encoder>
  </appender>

  <root level="INFO">
    <appender-ref ref="FILE" />
    <appender-ref ref="FILE2" />
  </root>
</configuration>