The manufacturer means something like 1'000'000h MTBF https://www.seagate.com/www-conten...

Thank you!

These drives will hast for years, they are specially designed for 7x24 h use in NAS systems. If you plan to buy a NAS, I advise to go with a 4 bay NAS, it will allow better expandability plus you could achieve e.g. 6TB usable disk space by adding 4 x 2TB drives whereas with a 2 bay NAS you would need to buy 2 x 6TB and if one of those fails, you need to buy another one. With a 2 bay NAS you basically have a 6TB drive for mirroring, when you do this with 4 x 2 TB then you only need 1 x 2 TB for redundancy data and you have much better use of your investment, even though the 4 Bay NAS may be a bit more expensive at first.