Each of my servers has 8Gb RAM and the memory usage hovers around 7Gb. I have a load balancer available to me but at the moment I'm worried that putting my sites through it will cause the platform to fall over. The load balancer would be configured with a sticky round-robin where a new connection is round robin but subsequent connections for the same source ip will remain on the same server (until a limit is reached). Thats all standard stuff.

How do I know what memory usage my sites will need across the platform when I put them through the load balancer? Rather than knowing that a site is using 150mb on a particular server I could face a situation where the 150mb is taken up on each of the servers. I know that with only 1 gb free I could have a serious problem on my hands. If I free up some memory then how can I work out what I need to have free to prevent this from happening?

Thanks Matt