The file server will have ( 2) 146GB RAID1 and (3) 146GB RAID5 disks."
Assuming the (2) 146Gb is for the system partition, this is much more space then needed for the OS and program files.
More efficient, get two (roughly) 73 Gig drives for the OS\programs, add the 146 GBs to the (3) drive raid 5. Not only do you get space, but for each drive added to a raid 5 (up to a point)your performance increases considerably, which will help offset the raid 5 write penalty.
"The TS will have (2) 146GB RAID1" This should be fine, depending on how many users login in total (as to user profile space needed). Generally with TS servers I have users with small local profiles, avoiding roaming profiles as to space and management headaches.
"I have a PowerEdge 2900 that has a Xeon dual core 5100 series and 2GB RAM that I could use as a second DC, would that suffice? I think 64 bit will run on it."
For the TS server, I would use the least horse-powered machine, ram is the most important factor on a TS, unless there will be many concurrent users. A PE 2900 with definitely run 64 bit, have a number running 64 Win 2008. Have a client who ran a PE 4600 TS (few concurrent users) which ran programs twice as fast as wks machines with almost triple CPU speed.
"Exchange (2) 146GB RAID1 and (4) 300GB RAID 10."
Again, for an Exchange server, 146 GB is way too much space.
Lastly I would purchase at least 1 spare 146GB and if you go down to 73s for the OS, one spare for that group.
No loss even if you have a 4 hour support contract, >3 years down the line drives become difficult to obtain, and expensive.
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