vServer performance issues after Joomla 1.6 installation

[odx]

Hello,
i ran into a really curious phenomena. I am running a vServer with ispcp.
I have currently 5 Joomla 1.5 installations on it. They perform quite well.

But as soon as i set up a Joomla 1.6 system the whole vserver begins to lag. This causes apache timeouts (resulting in error 500). Also the ftp server gets so slow that it cannot be accessed. (Email works but very slow..)

After removing the joomla installation (had to do that through ssh...) and restarting the services the server returns to normal operation.

I am not sure what is causing this bottleneck, even if it is up to Joomla or ispcp or maybe a combination of both.

AFAIK ispcp runs php in fastcgi mode. Maybe this is somehow related to this issue?
The server is equipped with 512MB of guaranteed RAM.

Has anybody seen things like this? I cannot really believe that a php system can cause the server to get this slow. But it happens definitely only with the Joomla 1.6 on my system so far.

Any ideas?

[RussW]

Has you run "top" or any server performance monitoring tools to determine how much resources are being used already? How much memory is MySQL, Apache, PHP using already, before adding the additional site? Maybe it's just too much for the resouces you have available/free. Have you tried another J1.5 site to see how much that might effect the perofmance? Not saying that J!1.6 isn't a hungry'er application than J!1.5, but maybe just one more DB app will tip the balance anyway.