Serving images through HTTP. Load balanced highly available architecture

I'm planning a system for serving image files from a server cluster with load-balancing. I'm battling with the architechture and whether to save the actual image files as blobs in the database or in filesystem.

My problem is that, the database connection is required anyways as the users need to be authenticated. Different users have access only to contents of their friends and items uploaded by themselves. Since the connection is required anyways, maybe the images could be retrieved from there aswell?

Images should be stored with no single point of failure. And obviously, the system should be fast.

For database approach: The database is separate from rest of my application, so my applications main database won't get bloated by all the images. Database would be easy to scale as I just need to add more servers to the cluster. Problem is, that I've heard this might be a slow system from a website with millions, even billions of photos.

For filesystem: I would be really interested in knowing how could one design a system, where the webservers are load balanced, and none of them is too important for the overall system. All the servers should use a common storage, so they can access the same files in the cluster.

What do you think? Which is the best solution in this case?

What kind of overall architechture and servers would you recommend for a image serving cluster? Note: This cluster only serves images. Applicatio开发者_如何学编程ns servers are a whole different story.

I definitely wouldn't store them in the database. If you need to use PHP for authentication, then do that as quickly as possible and use X-SendFile to hand over the actual image serving to your web server.

For the filesystem it sounds like MogileFS would be a good fit.

For the web server I'd suggest nginx. If you can adapt your authentication mechanism to use one of the existing modules, or write your own module for it, you could omit PHP completely (there's already a MogileFS client module).