Das geht über das maxArchiveFiles
-Attribut. Z. B.:
<?xml version="1.0" ?>
<nlog xmlns="http://www.nlog-project.org/schemas/NLog.xsd"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<targets>
<target name="file" xsi:type="File"
layout="${longdate} ${logger} ${message}${exception:format=ToString}"
fileName="${basedir}/logs/AppLog.${shortdate}.txt"
maxArchiveFiles="4"
archiveAboveSize="10240" />
</targets>
<rules>
<logger name="*" minlevel="Debug" writeTo="file" />
</rules>
</nlog>