Obviously to bring as much fiber as you need, but an average of how much bandwidth line you need to successfully startup your 1st data center?

How big is the data center? How many servers do you expect to house? What type of bandwidth will you be promising the owners (users) of those servers? Are you just concerned about capacity, what about redundancy?

Very good questions TRau.

The problem is Alan, much of what TRau asked, NEEDS to be asked before a solution or answer can be given.

There are far too many general variables involved, for there to be a straight answer that doesn't depend greatly on your own predetermined specifications.

Of course, say, 300 servers, and of course, we can't risk of not having that second pipe as the right hand man...

Ok. 300 servers - now still, what kind of bandwidth are you promising? I mean, you could host 300 servers on a cable connection. It might run slower than molasses at times, and some might not be "online" a lot of the time. But, you could do it.

"300 Servers". Still not much to go on, but let's say you are going to promise each server 10Mbs. Times 300 servers thats 3000Mbs capacity that you need in your datacenter. Thats the equivalent of an OC-48 + an OC-24 (ignoring overhead to keep things simple). You'll want multiple providers with multiple entry points into the facility. So again keeping it simple, let's say 5 OC-24 lines from 5 providers. That way you can lose any two lines and still provide the bandwidth promised.

How much startup capital do you have? This will be an important aspect to consider when you are developing a datacenter based on quality or price.

Like Trau said, you will need to make sure you keep multiple providers on the line, as you will lose a provider and you will want another to take its place.

Hope this helps.

Well,
about 2Gbit/s should do...
a bit of overselling wouldn't harm

I don't know about it.. I personally wouldn't oversell, especially being a data centre. If you couldn't provide enough and went over your limit, your going to be put in a rough spot.

I would agree there too much overselling of bandwidth would mean very slow and unstable speeds if anything you want to be looking in to having spare capacity available to you.

Thing is, it generally works the opposite way. Datacenters tend to be large enough for the laws of big numbers to start being applicable with quite a bit of certainty, hence making overselling an appealing idea, even more so given the amounts of money can potentially be saved.

Remember that one pair of fibre can get an awful lot down it using CWDM or DWDM. I personally would have 2 fibres coming in and ideally have these taken back to 2 major peering points (if you're not too far away from these) and have the fibres lit at gigabit (if you use CWDM it's relatively cheap to add more waves). I'd then route at the peering points and pick up transits there then use an IGP to handle failover at the DC end.