NLog – Archive by file size

To archive by file size when you’re using NLog, you can configure nlog.config like this:

<?xml version="1.0" encoding="utf-8" ?> <nlog xmlns="" xmlns:xsi="" xsi:schemaLocation=" NLog.xsd" autoReload="true"> <variable name ="logFile" value="C:/logs/servicelog-${shortdate}" /> <targets> <target xsi:type="File" name="mainLog" fileName="${logFile}.log" layout="${longdate} level=${level} message=${message}" keepFileOpen ="false" concurrentWrites ="true" archiveNumbering="DateAndSequence" archiveAboveSize="1000000" maxArchiveFiles="10"/> </targets> <rules> <logger name="*" minlevel="Trace" writeTo="mainLog" /> </rules> </nlog>
Code language: HTML, XML (xml)

You specify archiveAboveSize in bytes. The above configuration is specifying ~1 MB.

When your log file hits the specified size, NLog will “archive” the file, which really just means it will rename the log file and start a new log file. It will rename the log file based on the setting archiveNumbering. It’s a good idea to set maxArchiveFiles as well, so you don’t run out of disk space.

Example of archiving by log file size

I’m logging to a log file with the short date in the name. The log file is called servicelog-2021-02-22.log.

Once servicelog-2021-02-22.log hits ~1 MB, NLog will rename servicelog-2021-02-22.log to servicelog-2021-02-22.20210222.0.log (because archiveNumbering=DateAndSequence) and then create a new file called servicelog-2021-02-22.log, like this:

servicelog-2021-02-22.log servicelog-2021-02-22.20210222.0.log
Code language: plaintext (plaintext)

Let’s say I am logging all day and have 10 archived log files. Because maxArchiveFiles=10, when NLog has to archive again, it will delete the oldest archived file (servicelog-2021-02-22.20210222.0.log) and create the new archive log file with the next sequence number – servicelog-2021-02-22.20210222.10.log.

I’ll end up with the following log files:

servicelog-2021-02-22.log servicelog-2021-02-22.20210222.10.log servicelog-2021-02-22.20210222.9.log servicelog-2021-02-22.20210222.8.log servicelog-2021-02-22.20210222.7.log servicelog-2021-02-22.20210222.6.log servicelog-2021-02-22.20210222.5.log servicelog-2021-02-22.20210222.4.log servicelog-2021-02-22.20210222.3.log servicelog-2021-02-22.20210222.2.log servicelog-2021-02-22.20210222.1.log
Code language: plaintext (plaintext)

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