Subdomain or subdirectory

[CecilyP]

We're a big social networking site with over 1 million indexed pages and over 4 million visits a month. Our PR is 7.

We're about to acquire and rebrand the content of a large reviews website, current PR 3. The new content will be treated as a 'site within a site' with different navigation and interface.

With these factors in mind I think we need to create a new subdomain for the reviews site but I need to factor in the SEO implications, bearing in mind that new advertisers are going to be looking closely at our stats.

Migrating the content to a new subdomain I understand will be easier than siting it in a new folder.

Any advice appreciated

[RyanKent]

So despite the different look and navigation you recommend migrating the whole site to a subfolder on our subdomain?

If you own this site now I would suggest you take some time to investigate branding. A standard look and navigation is desired. On the other hand, you need to be careful making changes to successful platforms.

Based on what you have shared, the likely recommendation would be to use a subfolder, but a proper recommendation on such an important topic cannot be offered in a Q&A. A SEO would need to learn about your company, your business, your niche, the site you are absorbing, etc. prior to making a decision.

[CecilyP]

It's an existing reviews website with pretty good quality content -- and a good fit for our demographic.

We will re-brand the content and our users will add their own reviews.

So despite the different look and navigation you recommend migrating the whole site to a subfolder on our subdomain?

[RyanKent]

My main concern is the size of the new site and limits on the number of pages Google will crawl.

That should not be a concern. Google has the ability to crawl sites regardless of size. There are sites with millions of web pages. The largest forum site, http://www.gaiaonline.com/forum/index.php, has over 2 billion posts. I am not sure on the page count, but it's a lot.

Google will make whatever adjustments necessary to crawl quality content. The question is...do all of the pages on your site represent quality content? If your pages offer quality content, earn links, get tweeted / liked / +1'd, then Google will crawl them.

[CecilyP]

Thanks Ryan, really helpful and I'm starting to realise there are no definitive answers.

My main concern is the size of the new site and limits on the number of pages Google will crawl. This is not the only site within a site we're looking at.

[RyanKent]

It really depends on how closely you wish to integrate the reviews compared to your core social networking function. There are pros and cons to each approach. A great article on this topic:

http://www.seomoz.org/blog/understanding-root-domains-subdomains-vs-subfolders-microsites