I have two question:
- How many sites allow a WordPress Multisite installation.
- Probably it is a stupid question but, Is it possible to backup a specific Sub-domain in the multisite installation or you have to backup everything.
Backing up WordPress Multisite
The first part of your question doesn’t make sense. How many sites allow a Multisite installation? How many web hosts you mean? If so, who knows? Several thousand and there’s no way to keep track.
The second part of your question, Can I back up only one of the sub domains…. no. At least not in any meaningful way. Multisite shares the same database across all sites. I guess you might be able to do some sort of pattern searching in the database to do a backup on everything, but it’s such a narrow use case I’d be surprised if anyone bothered, and I’d be even more surprised if it was actually reliable. Keep in mind: multisite is one database, multiple subdomains. Some info, wp_users, wp_user_meta, etc are going to be needed in each of these little mini-sites, and the pattern matching you’d have to write to only keep users for your own site would be, to put it mildly, a pain in the butt. You’re better off just backing up everything. Exclude media files if you need to, but otherwise just back up the whole thing.
First part of your question is not entirely clear, but you probably mean somehting along the lines is there a limit of sites which you can create in WPMU. The limit is your server…If you have powerful and well configured server you can have hundreds of sites without a problem(don’t have an exact number though)
The only way to export a single site I can think of is by Going in Tools->Export and export the posts and settings as in a normal WordPress, but you’ll have to backup the uploaded files manually