Stuff you need to decide:
- Lots of smaller (1tb) disks or fewer larger (1.5tb-2tb) disks? Smaller disks are cheaper but will make the rig heavier/noisier/etc and will complicate later upgrades (all disks must be same size for RAID)
- Windows Server or Linux? Both work with Windows File Sharing or DC++ (though a bit buggy) or whatever; which you choose is a matter of preference and what you're more familiar with. Do not assume that once it's set up you can just leave it as it is; something WILL go wrong and you definitely want to be able to fix it yourself.
- Software or hardware RAID? Software RAID (connecting the drives through a SATA card normally) is easy to set up under Windows (and not that bad under Linux) but sucks up CPU and is sometimes unreliable. Dedicated hardware RAID cards are quite expensive, and their quality varies depending on how much you spend.
- Which RAID mode? There are several RAID modes which all give a different balance of speed and reliability. Generally for a setup like you're describing you'd use RAID-5 which gives good speeds and will allow recovery of your data if one drive fails.
If you're looking for a cheap (but still perfectly good) system, you can simply get any crappy old machine and throw a few SATA cards in it along with the drives and soft RAID it. SATA cards are cheap, crappy old computers are usually free and the cost of the drives is up to you. (Actually, I plan on doing this myself soon)
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