Every hard drive will fail sooner or later so if you don't already, please, please make copies of your photos!
I always make two copies before I delete them from my memory card. Ideally you also want one copy at a different physical location to your home although that's a little more tricky in practice for a big photo library.
The ideal so-called 3-2-1 solution means having a local copy, a remote physical copy and an online cloud back-up.
For the cloud back-up, there are a few no-cost options such as Amazon (if you're already a Prime subscriber), Google (if you don't mind Google reducing the size of each file) and Flickr (up to 1Tb). Or there are dedicated paid solutions such as IDrive, CrashPlan and Backblaze. A key issue though is the speed of your internet connection for uploading the images. If you're trying to back-up thousands of large files it will take a significant amount of time. I use Flickr at the moment, but only for a selected subset of my photos.
Whichever option you choose, work out a system that suits you, stick to it, and know that you'll always have a back-up copy of your photos when you need it.
Let me know if you have any questions I can help with. I hate to hear of photographers going through the pain of losing their images.