First, the link for two gems for every Multisite expert or wannabe or in-between.
WordPress Multisite 101
Setting up a new WordPress install is pretty easy. Setting up
Multisite requires just a little more savvy, and the information is
all over the place. This ebook strives to pull it all together,
explain you what skills you need to get started, and move you to the
next step: running your own Network. Think of it as a basic tutorial
in running your own Multisite.
WordPress Multisite 110
While it’s an extension of WordPress
Multisite 101, 110 isn’t a supplemental, in fact it’s longer than 101!
This is the next step for people who’ve managed to get the site up and
running, but want to do a little more. In this ebook, there’s more
philosophy and discussion, and fewer direct answers, because now you
have to make decisions based on the pros and cons. Are you ready?
These free1 e-books are written by no less than two giants of Multisite: Mika Epstein (aka Ipstenu) and Andrea Rennick.
Here's the snippet from the 101 that answers your question:
Subdomains vs Subfolders
A subdomain install means that your sites will look like this:
- Main site:
- Sub Site #1:
- Sub Site #2:
A subfolder install means your sites will look like this:
￼￼￼In addition, if you use a subfolder install, the post URLs on your
main site will have the slug /blog/ prepended to them, causing them to
look like this:
At this time, you cannot customize that slug, nor easily remove it.
There is no SEO benefit at this time to using subdomains or subfolders, and you can
map a domain name to either install, so the decision is purely
http://www.mattcutts.com/blog/subdomains-and-subdirectories/ for an
The Domain Mapping subject is extensively covered, so I'm pretty sure that the 101 reading will answer this and many other questions you may have.
1 Lot's of donation options in the e-book pages, choose the best that fits :)