Does anyone have any suggestion what to monitor. which tool is the best most relaible ...

it's a long time ago that I have worked on a aix system.

On a unix platform I would recommend to use sar to see what your system is doing. You probably want to use contrab to use sa every 20 mins to be able to see afterwards how busy your system was.

Not sure about top, is that available, usefull to see the actual status. Otherwise vmstat and iostat can be used.

Regards,
Han

AIX also provides a tool named "topas", giving you an actual status. There is also a freeware tool available "monitor", coming along with the option to write log files and some evaluation scripts

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Regards, Michael

Another free tool is NMON. I think you can find it on IBM site. We owe this tool to NIGEL. It's his monitor tool....
The latest version was 9. It is a nice tool with many options, I really like it.