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I am new to cdn but want an idea of bandwidth use so i can plan budgeting. I am starting a social network and want to use a CDN for static content and user photos. Let's say in total i have 15 javascript files and 10 css files for my site. I assume these will be hosted on the cdn and downloaded on each user's visit. Also user's have photos, so let's take each user uploads 200 photos at 100 KB each. There are 500,000 users. So 50,000,000 photos.

How much bandwidth will be used? The plans i see are like $30ish for 1 TB. Is that enough? Is there a chance i will need like 5 TB, 10 TB, etc?

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Presumably your javascript files are static and run on the client right? CDNs typically won't run active code on their boxes, purely static.

Anyway let's do the maths;

500,000 x 100KB is 50GB of data - they won't host that much but will happily cache it, so you need to host it on your origin server anyway.

As for bandwidth - well not everybody will download every image of course, so if you imaging that your 500k users will each download say no more than 100 images a day that gives us;

500,000 x 100 x 100KB - which is 5TB or 50Tb per day or 1.5Pb per month

Now users will cache images on their machines but things will become uncached and need redistributing, plus it should be quite bursty at the beginning so count on some large spikes every so often.

Hope this helps, quite curious what's your social network's unique selling point that you think will draw in 500k users by the way.

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Selling point - – Mani Feb 9 '11 at 22:04
I don't understand... – Chopper3 Feb 9 '11 at 22:06
oops forgot to type it. It is a professional networking site for information. Wont be useful to the lame people who post updates every 10 mins on facebook but it will be useful for the doctor or the lawyer or the programmer who wants to network, find information about his job related tasks, etc. Plus, unlike fb, my site does not 'rape' the privacy from people. – Mani Feb 9 '11 at 22:48
So, a bit more like LinkedIn then? – George Hewitt Feb 10 '11 at 8:23
No. Linkedin is very limited, you can't do anything with people you connect with except get a recommendation. Think of a hybrid between linkedin, facebook, yelp but Ad free and no locking people in unethically how these websites do. It is complex to explain here, you'll see it soon. Still a month away from launch hence trying to tie in all the hardware resources now. – Mani Feb 11 '11 at 20:40

Bandwidth in this context is a unit of consumption. ISPs and CDNs would usually refer to this as data transferred per month. So, it depends on how often your users visit.

If each photo was viewed once a month, with your numbers that gives around 4.8TB per month for photos alone.

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Generally you wouldn't host your web files on a CDN, but instead your static bulk payload (media, archives) files would be on a CDN.

I also think you're confusing bandwidth with capacity. To store 50 million photos whose size is 100KB each you'd need 5TB of capacity.

Hope this helps.

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