Issue the command WRKSYSACT. This will show you the jobs that are sucking the life out of the system and give you a place to begin....
From: John Mathew <johnmathew400@xxxxxxxxx>
To: Midrange Systems Technical Discussion <midrange-l@xxxxxxxxxxxx>
Sent: Friday, December 14, 2012 11:11 AM
Subject: Iseries System Extermely Busy.
For the last few weeks our iSeries system was extermely busy and the processing is very slow.
Can some one please guide me to check the following points in the system.
Increase in the number of interactive transactions
logical DB I/O's to disk.
Number of SQL jobs processed.
SQL I/O's to disk.
CPU Batch utilisation
Average transaction rate per hour.
Disk I/O's per second and CPU pool usage.