Solaris offers several tools for taking "snapshots" of system behavior. Although you can capture their output in files for later analysis, the tools listed below are primarily intended for monitoring system behavior in real time:
Watch the %b column to see how much of the time each disk is busy, and for any disk busy more than about 20% of the time pay attention to the service time as reported in the svct column. Other columns report the I/O operation rates, the amount of data transferred, and so on.
Monitor the sr column to keep track of the page scan rate and take action if it's too high (note that "too high" is very different for Solaris 8 and 9 than for earlier releases). Watch the us, sy, and id columns to see how heavily the CPUs are being used; remember that you need to keep plenty of CPU power in reserve to handle sudden bursts of activity. Also keep track of the r column to see how many threads are contending for CPU time; if this remains higher than about four times the number of CPUs, you may need to reduce the server's concurrency.