I have a website with 3.5M pages (one page for a product) but Google is only indexing about 1M pages according to google.com/webmasters
I was thinking of classifying these products in a few categories, say about 50 and use those categories as subdomains. For example:
Each product will show up under only one subdomain so that there's no duplicate content. I understand that Google treats subdomains as islands so there will be a rank hit if I do this. However, Google isn't indexing all pages anyway, so is this a good SEO approach? Can this actually increase traffic to 3X, given it would index all pages with this approach?