true clustering isn't done on application level, but on OS level. Our host sourceforge for example uses server clustering. We (as users who are hosted on their server cluster) don't notice the difference. So if you're looking for a real "pro" solution, you'll have to look for server clustering solution. A first step (on application level though) would be to have the mySQL database on another server than the actual PHP files, and the albums folder yet on another server (or even on multiple servers), using a symlink. To find good solutions, you'll have to find out first where the bottleneck is for you: is it computing power (as the script uses memory and burns cpu cycles), is it bandwidth, is it disk space or is it the database that lags? As mentioned in the other thread you started, there are third party tools that let you monitor all those data. For a workaround, you should reduce the detail level of your pages: less meta albums means less database queries, less pics to be delivered etc. There's a whole lot of optimization you could do before you actually have to think in a wider scale about server clustering. There have been discussions in the past about huge coppermine installs (with several 100,000 pics in the database and many gigs of traffic each day), you may want to search those threads (I think it was
Oasis who posted a lot in those threads, just to give you an idea what to search for).
Please post a link to your site as well, maybe we can spot some things that will improve your situation.