Notification is fine, automatically correcting problems is even better. A hung Web server process can be automatically restarted, a nearly full disk can have temporary files automatically cleaned off of it, or a flaky machine can be automatically rebooted. Automatically fixing as many problems as possible ensures minimum down time, and reduces the need for human intervention. Collecting and Using Historical Data Historical data allows the correlation of several sets of monitor readings, leading to a quicker diagnosis of problems. For example, if the CPU utilization of the Web server machine is very high, then failures to retrieve URLs during that period of time may be related to Web server overload rather than the failure of the Web server process itself.
Historical data can also uncover trends that are useful in preventative maintenance.
If a disk space usage monitor indicates a disk is filling up, steps can be taken to determine the root cause well before the problem becomes critical. Cyclical patterns of usage may also be revealed. A nightly maintenance process might be creating temporary files that bring the disk perilously close to capacity, and then delete those files before anyone notices. Here's an real world example that illustrates the usefulness of having a history of a server's performance. A web administrator who had been running automated monitoring software was sure that there was something wrong with the monitoring setup - requests for web pages from his server were shown as timing out at the top of every hour, and he hadn't heard any complaints from his users.