When monitoring Microsoft® SQL Server™ and the operating system to investigate performance-related issues, there are three main areas on which to concentrate your initial efforts:
It can be useful to monitor Microsoft Windows NT® and SQL Server counters at the same time to determine any correlation between the performance of SQL Server and Windows NT. For example, monitoring the Windows NT disk I/O counters and the SQL Server Buffer Manager counters at the same time can show how the whole system is behaving.
Monitoring a computer using Windows NT Performance Monitor can slightly impact the performance of the computer being monitored. Therefore, either log the generated Performance Monitor data to another disk or computer so that it reduces the effect on the computer being monitored, or run Windows NT Performance Monitor remotely. Additionally, only monitor the counters in which you are interested.
Monitoring too many counters adds overhead to the monitoring process and will affect the computer being monitored, possibly affecting the results produced.