I would think using some sort of raid 1 or 5 setup would be best for you. Like they said SSD are very expensive and like all things, they can fail too.
Might I suggest a Buffalo Links station. We have 2 of them for datastores. Since the data is not that crucial, we only run a Raid 1 with Hot Swappable drives. But they do sell larger units as well. They are very easy to setup and seem to perform well. There also other brands that do the same thing.
If your files are extremely valuable, you could buy an removable sata device like a Removable SATA hard drive bay and do backups to the drive and take them offsite to a bank vault like I do.
Just some thoughts.
Rodeoboy