The WD Purple HDD 4TB is highly recommended in this forum. I bought one and copied all my data into it only to find out that the HDD is too big and won't fit the HD space of my All in One Dell Optiplex desktop. I got this back in February so I doubt I can return it. Should I just get a smaller HDD and if so, which one do you recommend? Or can I just use this one as an external HDD instead? Thirdly, can I still use the computer the same as it was even after mirroring the HDD to the WD Purple HDD?