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I'm guessing that I'll need to add a RAID controlller card to the PC correct?


Not if you don't want to. Linux will use software RAID over your existing disks. I don't know what's involved with getting software RAID on Windows, though -- you might need Windows Server.

Otherwise, you can pick up Highpoint or Promise RAID cards for not a lot of money.

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Are the prices for these things anywhere close to reasonable?


Depends on what you mean by reasonable. When I went for RAID5, I picked up a 3ware SATA card, 3ware's hotswap SATA cage (it takes 4 drives and fits in 3x5.25" bays -- it includes the drive trays), and 4x200Gb Seagate Barracuda disks, it came to around £700 as I recall. This was about 3-4 months ago.

You can spend less by opting for a cheaper card (e.g. the Promise) and by not using a swappable cage.

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If the cost is prohibitive, I suppose I could just get the 400GB plus a DVD burner and back-up onto DVDs...


If you're just dealing with music (or other content that doesn't change that often), this might be the right thing for you. Burning DVDs takes an age, and you have to be there to swap DVD-Rs. If your content doesn't change very often, then you only have to do this every couple of weeks. If you're backing up other stuff, I think you'll soon get bored with it.
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-- roger