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Well, it's been a nightmare day for Zope on our box. Does it self destruct when Data.fs reachs a certain size or something ?

There are no built-in limits on Data.fs size. Your OS may have one however. How big is the file?

Small - 50 MB. My above comment was more of an inane introduction, sorry. I didn't really think this could be the cause.

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"Temporarily Unavailable The resource you requested is temporarily unavailable - please try again later. (116) unable to connect, fd=3 "

PCGI cannot connect to Zope. Can you connect to ZServer?

No, we could not connect to the Zserver directly.

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Alternatively, the server just hangs and doesn't respond (but ps -aux shows the process is running).

Is it spinning? (consuming 100% CPU resources?) or hung? (consuming none..)

Sorry, you're right, it was 'spinning' - 100% CPU resources. Does that suggest anything in particular ? When this first occured, I restarted Zope. That solved the problem for a few hours but problems kept recurring. Last night I restarted the server and since then it has been OK (for the past 8 hrs) ... but I'm anxious how it will stand up to being put under load again today. chas