Steam Pushes Over 3/4 of a Terabit on Their CDN

The Steam Summer Sale is upon us once again. I, like many Steam users, look forward to these seasonal events. Unlike most Steam users though (I assume), I have a constant fascination with the Steam Content Server Stats page. I like watching the trends and seeing just how much bandwidth the Steam CDN can eat up, keeping a mental note of the highest peak utilization.

In terms of the trend, utilization is often around 200 - 300 Gbps, sometimes dipping below 200 when there’s nothing particularly exciting happening (e.g. a not-so-great midweek sale). Prior to the sale, the highest I had ever seen the peak value was 658 Gbps. The sales are often the record breakers and this summer did not disappoint. Below is a screen capture showing a peak of over 768 Gbps, 3/4th’s of a terabit.

Even the smaller of those numbers is nothing to sneeze at. That’s a lot of bandwidth. In late 2010 when Netflix announced a move to Level 3 for streaming of their video services, Level 3 stated that they had 1.65 terabits of global CDN bandwidth with plans to add 2.9 Tbps more. Now, that’s not just the bandwidth allocated to Netflix but Level 3’s entire global CDN which serves various other customers. Granted we all pretty much know Steam is not small in terms of users, but this just further shows that they are definitely playing with the big boys here. (Today, Level 3 boasts a total 5.6 Tbps of global capacity, with today’s numbers Steam could still eat a huge chunk of that if they used Level 3 exclusively).


I was initially thinking about holding off writing this post up as there is a good possibility for Steam’s current throughput record to be broken as we are just starting the summer sale. However, I don’t think it can be beat by much.  Looking at the individual server loads, you can see many of them are being pushed to the max. While the demand could very well be capable of using up over a terabit, it doesn’t look like Steam could provide it without adding more servers. The images below show the demand that the Summer Sale has brought on the network.

I’d personally love to read up on some details of Steam’s CDN, something like a High Scalability post. It’s not clear to what extent (if any) Valve runs their own content servers or utilizes other company CDN/cloud services.  I did find information on Valve using Highwinds’ CDN for some of their Steam traffic. The majority of Steam traffic may even utilize Highwinds, though the article is not specific. I’m somewhat surprised at this since CDN pricing is usually seen as a bit high, so they must be getting a good volume discount. I remember once tracking an IP that my Steam client was connected on to Limelight Networks, so multiple cloud providers are probably at work here. If so, why the hard limit on individual servers (whatever those may be)? Why slow download speeds during sales? Could Steam actually be placing that much load on multiple cloud providers? Perhaps, but those providers are not likely to let their other customers be drastically affected due to the demand of one other customer.  My guess is that there is some sort of throttling going on as part of the negotiations. But whatever it may be, Valve certainly knows what they’re doing.