Over at the Wall Street Journal and Micro Persuasion and Computers.net and a bunch of other places, a big deal is being made of the YouTube’s estimated 45 Terabytes worth of video. It is “about 5,000 home computers’ worth”. Ouch, 45 Terabytes! Wow!
Or maybe not… consider the mathematics.
45 TB really isn’t all that much data. I’ll assume that each video is stored on 6 hard drives across their systems, for reliability and greater bandwidth, for a total of ~300 TB of hard drives. A 300 GB hard drive costs under $200, and ~1000 will be needed, so this is about $200,000 worth of hard drives, which is not a big deal for a major venture-funded firm like YouTube. (Side note – if you need a lot of read-mostly disk bandwidth, you are much better off buying several cheap hard drives with the same data on them, than one expensive hard drive. It’s not even close.)
The 1000 hard drives might be spread across 250 servers. If their systems is build in the economically smart way (the Google way – lots of commodity servers), each server could cost as little as $3000. Those servers could likely serve the traffic also, as well as (at a lower priority) do any needed video transcoding of newly uploaded video. After all, it is mostly static content, and it’s likely that a small fraction of the videos are a large fraction of the views, so the popular ones stay in RAM cache. Adding other machines for various purposes, network hardware, etc., a YouTube-scale app/storage cluster might cost as little as $2 million, of which a relative small portion (above) is hard drives.
Of course I’ve totally skipped the question of paying for the bandwidth (and power), which must be staggeringly expensive.