I get asked this a lot from a more technical perspective.
All the myriad reasons you have to use, or not use, Multisite aside, the question that is often wondered and confused over is the one where we’re trying to balance out ease of support vs cost. You see, a lot of the time, people consider multisite because they’re on a webhost who only allows one domain for your site. You may be able to use add-on domains but they also may be limited, and the easiest way to run a hundred sites on one hosting plan is multisite.
I have to remind everyone here, I would never, ever, in the history of ever even remotely consider running Multisite on anything less than a VPS. Yes. I said it. Keep in mind when I run a Multisite I’m always doing it to run a network of heavy duty sites. If I was just running a tiny private network, my goals would be different. But more than that, I keep in mind the realizations of the limitations of shared hosting. Shared hosted is tiny. Multisite is big. Match ’em up and you’ll be happier.
What does this have to do with the heft of a network? Well if I have 100 separate sites and 100 sites on a multisite network, what’s the real, practical difference?
- 100 separate logins vs 1 login on 100 sites
- 100 separate sites to update vs 1 site
That’s pretty much it. Yes, there are a dozen of little things (like it’s easier to restrict access to a single site) that come into play here, but when you start looking at the server itself, the practical differences when it comes to things like disk space, memory usage, process utilization, and emails, there is no negligible differentiation on your site’s performance.
Yeah, 100 separate sites and 100 sites on a network will run pretty much the same on the same server, assuming the exact same level of traffic and use of plugins. That’s a pretty big assumption most of the time but in this one case, it’s safe. We’re trying to compare apples and apples, with only one difference: Multisite or Not.
Of course, there are specific situations where a multisite will cause more damage to a server than a single site, especially if you’re doing a lot of cross-content manipulation (like including the RSS from one site into the sidebar of another). But it all really depends on if you have a lot of traffic. Yes, one Multisite blog getting hammered will hurt the others on the network, but it shouldn’t cause a significant CPU spike any more than two separate really massive single sites would on the same server.
And there is one place where Multisite very much would do more work on the server than Single Site, and that’s with ms-files.php. That old magic that made your image URLs to be domain.com/files/2014/09/image.job. The way that worked was to pass images via .htaccess through the ms-files.php page and then generate the image. Yes, that caused more load. It’s part of why we don’t do it anymore, and why I suggest never trying that again.
It’s funny, though. I’ve seen one host say that Multisite will use less by way of PHP processes because it’s one install, while another said it would use more because ‘Multisite’, and a third said there’s no difference.
Obviously I don’t think there’s a difference.