Which task is considered proactive maintenance for a Windows Server 2019 machine?

Proactive maintenance involves taking measures that prevent issues before they arise, ensuring the overall health and performance of the system. Ensuring that 20% free space is always available for file caches is a proactive approach because it helps to maintain the performance of the server. Insufficient disk space can lead to system slowdowns, application errors, and even crashes. By keeping this buffer of free space, administrators can prevent problems related to disk utilization, such as fragmentation and performance degradation, before they impact the server's functionality.

The other tasks mentioned, while important, are reactive or do not directly contribute to preventing future issues. Gathering information about problems is a reactive step taken after an issue occurs. Documenting solutions to problems provides valuable insights for future incidents but does not prevent issues from happening in the first place. Monitoring the system and taking backups can provide recovery options but, like the first task, does not proactively address potential underlying issues.