I came across a user review of the DNS-343 4 bay D-link NAS. This is a low price four bay nas that is quite hackable as are all the D-link NAS devices due to the fun_plug.

Fun_plug is described as:

Fun_plug is essentially a technique to stepwise turn a NAS with fixed out-of-the-box functionality into an open Linux machine on which you can install additional software packages and, if you want, learn a bit about Linux.

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