I am buying a 9 bay esata enclosure and PCI-X ESATA RAID controller. My plan is to put 9 2TB drives into it and run a RAID-5 setup with it on my Win2k8 32bit Enterprise server.
I have heard a lot of different stories about which drives to buy or not buy for my purpose (get as much RAID 5 space as I possibly can). What drives should I go with: Samsung SpinPoint HD204WI, WD Green 2tb or the Seagate Barracudas?
RAID-5 is not a good choice for that large an array - at those sizes you've got too big a chance of not being able to recover from a drive failure.
The reason for this is that if you loose a drive in a RAID-5 array then the only way to recover the data is to read every byte from all eight of the remaining drives. That means you have to be able to successfully read 16TB of data (about 10^14 bits) without errors.
Hard drives often have unrecoverable read error rates of about one in every 10^14 bits read - that means you're almost likely to encounter a read error and therefore won't be able to recover your data.
RAID-6 is a much better choice because it uses two parity drives - you have to loose two disks simultaneously before you're dependent on all the drives being able to deliver all of the data correctly.
If you need to build an array that large then either use RAID-6, or at the very least make sure you find drives with as low an unrecoverable read error rate as possible. Most enterprise-class drives are spec'd at one read error per 10^15 bits read, about 10 times better then many consumer drives.
The other thing to beware of is that with 9 hard drives in an array you're fairly likely to experience a failure within a few years, and the performance of the array will be very poor when it's operating with a failed drive. Not only that, but it will take a very long time (possibly days) to rebuild an array with so much capacity. If this is being used for a business then you need to make sure that it can tolerate the reduced performance over that period of time.