What fiber should I run between 2 floors in a company site?

I'm helping a customer in moving his company to a new building. There we'll have two racks on two different floors to accomodate various servers and switch infrastructure. We'all also use the opportunity to migrate the last remaining 100mbits portions of the network up to gigabit speeds, the whole setup will be Cat.6 certified.

We don't currently use any fiber (nor do I have experience with) and our switches are all copper, but I'm thinking to get some between the two racks, to have the possibility to use that as 'backbone' in future expansions (network cables are distributed between the two racks, so I get some switches in one rack and some in the other). There's some 30~40 meters of conduits between the two racks.

• do you think it's a good idea?
• how many pairs should I get?
• is it correct to think in pairs at all?
• what fiber type, what connector?

I'm mostly thinking about upgrades in some years when 10gbit will get into companies, maybe just starting as backbone between gigabit copper switches when gigabit will start to get pushed by end user systems. Seems like the most common and price-wise option is to think about switches with GBIC or the like slots.

From serverfault Luke404

• Fiber is an excellent way of avoiding electric coupling between floors. For that short a distance and within a building, I'd personally consider multi-mode (usually cheaper GBICs and slightly cheaper cable). However, if you're not concerned about galvanic isolation, it's absolutely fine to go for copper.

  As far as connectors go, you'll be wanting whatever suits the switch. There are (or at least used to be) patch cables you could use to change from ST to SC presentation, wouldn't be surprised if that's available for the smaller connectors commonly seen today.

  Fibers are normally used in pair (one transmitting one way and the other transmitting the other way), so thinking in pairs isn't a bad idea.

  In my experience, the cost of the fiber is pretty small in comparison with the cost of getting it installed, so if you're wanting fiber, you're probably better off installing "what you think you need, plus a little extra" (so if you think you'll just need one pair, you might as well install 2 or 4, if you think you'll only need 3 pairs, you may as well install 5-8).

  Bart Silverstrim : For fiber, I'd always have MORE than enough pairs. We've had pairs installed and "certified" then later had them mysteriously stop working, so we have to switch to another set of pairs. Those extra dark pairs have been hair-savers.
  From Vatine