Hello. I'm creating a SaaS offer where each customer will have its own subdomain-based URL (i.e customername.mydomain.com). This subdomain will have several URLs, fixed as customername.mydomain.com/contact and variable pages customername.mydomain.com/page1. All those pages should be indexed by Google. What's the best way to do so? - should I create an only sitemap.xml at www.mydomain.com/sitemap.xml with ALL pages from *.mydomain.com? or - should I have to generate an unique sitemap for each subdomain? If I have to create this unique sitemap, I'll have hundreds of sitemap URL to submit to google webmasters tool. How to proceed with that? Thanks a lot!
http://support.google.com/webmasters/bin/answer.py?hl=en&answer=75712&topic=8476&ctx=topic you can have one sitemap but you need to verify each subdomain Sitemaps are largely redundant on very small sites, google can index them quickly and accurately once they find links from somewhere else - so all you need is a "directory" on your www subdomain that googlebot can check for updates - it can be generated from your database so you don't need to maintain it.
So I can have only one sitemap, database-generated. perfect. But I won't link subdomains from w3... will this work? What do you mean with directory to googlebot? Is there anyway to submit and verify those subdomains in batch?
Aaah, no you can many - even for the same site which allows for people operating multiple cms systems on the one domain with each cms generating it's own sitemap. I reckon most people like to keep it simple and have just the one although if your cms is generating them there's no extra work once you've verified the domain and given the sitemap links. I don't know any shortcuts around the submit and verify process, others might?
I can have both mydomain.com/sitemap.xml or subdomain.mydomain.com/sitemap.xml which one is the best way? would be this enough to be indexed?
Neither are best - the key is which you will find the easiest to manage as your site grows - it's about what works for you. They will be enough to get indexed but not to do well in the SERPs
If the subdomains are referenced in the sitemap, yes... did you read the official google docs at that link I posted?