Growing at over 30% a month has not been without challenges. Some reliability problems among them. It helps to realize that Tumblr operates at surprisingly huge scales: 500 million page views a day, a peak rate of ~40k requests per second, ~3TB of new data to store a day, all running on 1000+ servers.
— Tumblr Architecture - 15 Billion Page Views A Month And Harder To Scale Than Twitter
(Source: highscalability.com)
