Thanks for your answers.I am not sure if Vu+ uno 4k SE is capable of Sata3, but even if it's not capable I think it should be compatible with a sata3 drive?By looking at your answers and my quick web search, I think sata2 or sata3 hdd drive is really not important, a sata3 hdd doesn't bring advantage.
Actually I'm in between two hdd drives, one of them is a Toshiba L200 2.5inches Sata2 1TB 8mb cache internal hdd, the other one is a Seagate Mobile 1TB 2.5" Sata3 128MB cache internal hdd.They are almost at the same price, 128mb cache looks good over just 8mb cache of Toshiba's hdd, but if it isn't an important advantage for a Vu+, I may prefer Toshiba one cause I like that brand.