Why would you want to run a file server off a Raspberry Pi? Maybe you want a small server that is always on and low voltage. If you need something that you can send and recieve files to and from than this might be your solution. The Raspberry Pi is low voltage running at just 5.0V ±5%. This means that your server will end up costing you around $5 a year.
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Raspberry Pi NAS (CMDann.ca)