Bit-Tech writes: "Unless you're a digital hoarder who has more porn media than you can shake a DVD collection at, two terabytes (or more in the future) is plenty for most people as a bit of communal storage. Four disk NAS boxes are expensive and simply excessive for many, so what can you get for just a pair of drives?
Not everyone requires the storage space of a Google data centre, and a couple of drives, either just offering the total space or a mirror of each other for some peace of mind. Having the drives outside the main PC means there is no chance of them dying should the PSU pop, and leaving on a smaller, low power device is far more economical than leaving your big hunky PC running all day and night.
A two disk NAS box does limit the data storage options available though. With just a pair of drives, RAID 5 or 6 is unavailable, so data redundancy can only be achieved with RAID 1 but then you lose half your total capacity and achieve no extra performance. RAID 0 will give you the full capacity (with some overhead) and better performance but it will also double the risk of losing your data. JBOD is respectively safer for allowing the full capacity and "safer" than RAID 0, but it still has no data redundancy or extra performance."