WRKSYSSTS - Work with System Status
WRKDSKSTS - Work with Disk Status
RTVDSKINF (Must be run in batch)
PRTDSKINF (Works in conjunction with RVTDSKINF)
There are also many third party tools that can help you with this.
For further information you can read Chapter 7 - OS/400 disk storage management tools in AS/400 Disk Storage Topics and Tools.
Dig Deeper on iSeries system performance and monitoring
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