How much storage does a Pastebin-like service need over 3 years?

The scenario

You’re sizing storage for a Pastebin-like service: users paste blocks of text, receive a short URL, and the content lives until it expires. No image hosting — text only.

The service has 10 million users generating 10 million paste writes per month (10:1 read-to-write ratio). A typical paste is about 1 KB of content.

How much total storage (metadata + content) does the service need to cover 3 years of data?

Adapted from: donnemartin/system-design-primer — Design Pastebin.com — CC BY 4.0