Looking at [the Logback demo page][1] the following works for the 'CyclicBufferAppender':

    <appender name="CYCLIC" class="ch.qos.logback.core.read.CyclicBufferAppender">
      <MaxSize>512</MaxSize>
    </appender>

I have not tried it, but this may also be the same syntax for the RollingFileAppender.


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**[UPDATE BELOW]**

The following XML is also given on the logback site.  This uses the RollingFileAppender suggests that the 'maxFileSize' element needs to be inside a 'triggeringPolicy':

    <configuration>
      <appender name="FILE" class="ch.qos.logback.core.rolling.RollingFileAppender">
        <file>test.log</file>
    
        <rollingPolicy class="ch.qos.logback.core.rolling.FixedWindowRollingPolicy">
          <fileNamePattern>tests.%i.log.zip</fileNamePattern>
          <minIndex>1</minIndex>
          <maxIndex>3</maxIndex>
        </rollingPolicy>
    
        <triggeringPolicy class="ch.qos.logback.core.rolling.SizeBasedTriggeringPolicy">
          <maxFileSize>5MB</maxFileSize>
        </triggeringPolicy>
        <encoder>
          <pattern>%-4relative [%thread] %-5level %logger{35} - %msg%n</pattern>
        </encoder>
      </appender>
            
      <root level="DEBUG">
        <appender-ref ref="FILE" />
      </root>
    </configuration>



**The following information is also given [on the site][2] too:**

Specified number is not in proper int form, or not expected format.

When you specify the MaxFileSize to be used by the SizeBasedRollingPolicy, logback expects a rather precise format:

The number has to be an integer
You can add 'KB', 'MB' or 'GB' after the number.
Here are some correct values: 500KB, 15MB, 2GB.


  [1]: http://logback.qos.ch/demo.html
  [2]: http://logback.qos.ch/codes.html