Storing 5TB web server access log vs OLAP DB
I recommend Vertica.

You can get the free community edition that allows up to 1TB of data. If you normalize your web logs when you load them in, chances are they'd compress down and may fit under 1TB, as Vertica has a pretty powerful data compression engine itself.

If not, I'd still recommend trying out the platform, but the license fee isn't the cheapest thing in the world.