We want to scan the *complete data in less than 1 hour* - which is possible with our direct attached storage now
I question this, but will bow to your experience. Ultimately *everything* which can be achieved using local attached storage can be achieved using a SAN, and more. SAN is more expensive that Direct Attached, but is significantly more flexible and capable.
In the future we will have 10 to 100 times more data, so we would need a network for 10 GBytes per second to 100GBytes per second and we would need 20 to 200 quadcore CPUs for that.
At this point my recommendation becomes really simple. If you are going to be getting that much hardware then get the pre-sales storage architects from HP / IBM / EMC into your office and explain that you are about to spend a LOT of money with them. When they have finished drooling over you, sit them down and explain the problem. Get them to provide a solution with a written performance guarantee.
Could you give me an example how this can be done? Even if the SAN can do this, we would need a cluster of 10 to 100 servers for the needed number of CPUs.
Not without spending a lot more time on this, and I would still recommend getting one of the SAN vendors in.