Backing up your computer files is something everyone should have a strategy for doing... not just photographers. Unfortunately, few folks do. And if you do, is your strategy an adequate one?
Why one should have a backup strategy?
File storage devices fail. It's not a matter of IF they will fail but WHEN they will fail. This held true for the floppy disks and tape storage of old. In today's world, it holds true for HDD's and SSD's as well.
So what is the solution? BACKUP, BACKUP, BACKUP
What kind of scenarios necessitate the need for a backup?
The most likely scenario is a failing or failed HDD. If you have a working copy of what was on that failed HDD, you can simply purchase a replacement drive, copy the files from the backup HDD to the new one and you are back in business.
A less likely cause, is a catastrophic event such as a burglary, house fire, flood or whatever. In this case, a third HDD stored in another location can save your bacon. An alternate to this is utilizing a cloud backup service.
I have been reluctant to utilize a cloud approach for this third backup due to the length of time it would take to upload the many, many, many photos I have. As of this writing, I have approximately 1250 GB of files.
My Desktop Backup Strategy
In short, my backup strategy consists of multiple copies of my files on multiple HDD's. On my desktop computer, my second internal HDD is a duplicate of the first internal HDD. I have an external USB powered HDD that I will use for a third copy. That HDD is stored in my safe deposit box at my bank.
The contents of the third HDD are not as current as the second internal HDD on my desktop computer. I only update the third HDD twice per year... prior to leaving for Driggs and upon my return from Driggs.
My Laptop Backup Strategy
When I am on the road, I take along two external USB powered HDD's and use them in the same manner as my desktop internal HDD's.
By the way, I do not delete the RAW files from my card until I have assured myself that I have a valid copy on my HDD's. I then format that card in my camera rather than simply deleting those photos while the card is connected to the computer.