I had about a million pages of a catalog indexed under a subdirectory, and now that's moved to a subdomain. GoogleBot is crawling each one of them and getting a 301 redirect to the new location. Even though I have set up the redirect rule in the apache sites-enabled configuration file, (i.e. it's early on when apache does the redirect - PHP is not even getting loaded), even though I have done that, the server isn't handling the load well. GoogleBot is making around 5 requests per second, and on top of my normal traffic that is hiking up the CPU for a few hours at a time.

I checked in Webmaster Tools and the corresponding documentation for a way to let Google know that the content had been moved from a subdirectory to a subdomain, but with little luck. Basically the most helpful thing I saw said to just send 301 headers for the new location.

How can I tell GoogleBot that a subdirectory is now a subdomain? If that is not an option, how can I more efficiently send 301 redirects out for a particular subdomain?

I was thinking perhaps the Nginx server but I'm not sure that I can run both Apache and Nginx side by side on port 80 for different subdomains.