Have you ever heard about the 'Human Brain Project' ?

Well, they produce 100 GB of data _per second_

Welcome to the real big data world.

Maybe it includes images.

Pick a topic you are familiar with. Open up a twitter search for it. Wait a while. See the inevitable storm of tweet-spam that sort of looks like social sharing.

Thousands of fake accounts are tweeting out nonsense all the time. Another example, there are multiple accounts that tweet items from HN (and presumably lots of other rss feeds).

Depends how much metadata there is with every tweet.

I took a random tweet on my timeline, and the JSON representation, with added metadata, weighs 8740 bytes.

With this figure, you would "only" need 500 tweets/sec to get 400GB a day.

There's a lot of people on Twitter, and a lot of bots, so that doesn't seem unreasonable to me.

Most of that data is not the content of the tweet itself, but the metadata associated with it. When I last checked, we were storing about a kilobyte of data for every tweet.

Also, tweets are limited to 140 characters, not bytes - chinese tweets typically take about 200-250 bytes, for example.

I have access to the Twitter gardenhose (which is equal to slightly less than 10% of the full volume). These are the RX and TX statistics from the machine that I've been using to gather data for a few months now:

RX bytes:18053724505080 (16.4 TiB) TX bytes:2686623557042 (2.4 TiB)

It works out at around 70GB/day, so I'd actually think that the full firehose would use considerably more data than 400GB/day (likely closer to 800GB).