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With respect to hardware for a new system, knowing your use case and desired storage capacity is required. You can't easily add a hard drive to increase the capacity with ZFS. There are little things that need to be planned in advance. Hardware wise if you stick to a motherboard that is common (like the one in my signature) and then get a CPU that will have the horsepower you need, matched with some ECC RAM, you will do fine. These are the common parts people like to cut corners on because they are not the cheapest items but honestly, the hard drives are the most expensive single component and you expect them to fail after a few years of use (warranty period). Again, know what you expect the system to do and the capacity you will need.
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