isapi_redirect.log file too big

Dani, there's a bit more you should consider:

First, to your question to Priyank, no, it would not. But if you renamed the log file, while cf and iis were down, then when they were restarted a new log would be created.

Second, while I agree that you should check the log level, if it's already set to info, you should assess what is in the file in recent minutes, hours, and days. If there are errors  you'll want to address them.

Third, you had asked also if there is a way to control the size. There is indeed, as another line you could set in that properties file, log_filesize, which will rotate the files when they reach that size. Or you can instead set them to rotate based on time with log_rotationtime.

For more on these and still other directives  see the Tomcat directives at:

The Apache Tomcat Connectors - Reference Guide (1.2.x) - Configuring the ISAPI redirector for Microsoft IIS

(To be clear, CFs web connector is indeed the Tomcat web connector and recent CF versions and updates do use a connector whose version is 1.2.something--depending on the cf version and update levek, so these are indeed the docs for us to follow.)