Thanks for the help.
However, four words which create a lot of work......
No chance to restore a part of system files, where the mdworker stuff is located from a backup?
Reinstallation is kind of a ultimo ratio, easy said, cumbersome to do, especially on a server, with all the setup, passwords etc....
TL;DR: Check the console logs for errors.
Spotlight isn't specific to OS X Server.
Reinstalling OS X and OS X Server isn't a huge project and is a common solution for some variations of "weird" but wouldn't be my first choice here.
I'd start with a look at the console log files first and see what (if anything) is logged there around mdworker et al.
I've seen cases where odd-ball or corrupted files can trip up Spotlight, though finding those files can sometimes be a little interesting. If it's a user's file that's tripping Spotlight, reinstalling OS X Server doesn't help.
Later versions of Spotlight tend to work a little better, though I'm guessing there's a reason you're still at 10.6.8.
Thanks for all replies.
Meanwhile I tried the following:
- I had a second hard disk HD2 with an older clone of HD1. I launched the server with this Volume and here mdworker was running
- existing files where not indexed here, new ones or duplcated ones yes
I was happy to see Spotlight working, but since some days again, mdworker died....
I will give Onyx a try....