Where does youtube store so many videos?

Solution 1:

Google doesn't just store a lot of data on a lot of servers, they have written software that distributes the load and storage automatically, while recovering from hardware faults transparently (like BigTable and Map/Reduce).

The alternative is: a. You use someone else's infrastructure (Amazon S3, Akami) b. You use expensive storage vendor's products (NetApp) c. You write your own system similar to Google's

Facebook recently switched from a combination of A and B to C for their photo storage as it grew to unmanageable proportions.

Solution 2:

Content Distribution Networks (large clusters of servers at geographically distinct locations) are the key for any data and/or traffic intensive web-scale app.