Years ago, we called Dropbox a “Magic Pocket” because it was designed to keep all your files in one convenient place. Dropbox has evolved from that simple beginning to become one of the most powerful and ubiquitous collaboration platforms in the world. And when our scale required building our own dedicated storage infrastructure, we named the project “Magic Pocket.” Two and a half years later, we’re excited to announce that we’re now storing and serving over 90% of our users’ data on our custom-built infrastructure.

Dropbox was founded by engineers, and the ethos of technical innovation is fundamental to our culture. For our users, this means that we’ve created a product that just works. But there’s a lot that happens behind the scenes to create that simple user experience.

We’ve grown enormously since launching in 2008, surpassing 500 million signups and 500 petabytes (i.e., 5 followed by 17 zeroes!) of user data. That’s almost 14,000 times the text of all the books in the Library of Congress. To give you a sense of the incredible growth we’ve experienced, we had only about 40 petabytes of user data when I joined in 2012. In the 4 years since, we’ve seen over 12x growth.

Dropbox stores two kinds of data: file content and metadata about files and users. We’ve always had a hybrid cloud architecture, hosting metadata and our web servers in data centers we manage, and storing file content on Amazon. We were an early adopter of Amazon S3, which provided us with the ability to scale our operations rapidly and reliably. Amazon Web Services has, and continues to be, an invaluable partner—we couldn’t have grown as fast as we did without a service like AWS.

As the needs of our users and customers kept growing, we decided to invest seriously in building our own in-house storage system. There were a couple reasons behind this decision. First, one of our key product differentiators is performance. Bringing storage in-house allows us to customize the entire stack end-to-end and improve performance for our particular use case. Second, as one of the world’s leading providers of cloud services, our use case for block storage is unique. We can leverage our scale and particular use case to customize both the hardware and software, resulting in better unit economics.

We knew we’d be building one of only a handful of exabyte-scale storage systems in the world. It was clear to us from the beginning that we’d have to build everything from scratch, since there’s nothing in the open source community that’s proven to work reliably at our scale. Few companies in the world have the same requirements for scale of storage as we do. And even fewer have higher standards for safety and security. We built reliability and security into our design from the start, ensuring that the system stores the data in a safe and secure manner, and is highly available. The data is encrypted at rest, and the system is designed to provide annual data durability of over 99.9999999999%, and availability of over 99.99%.