As a long time photographer I have the same issue as most photographers. Years ago I stored my photos on CD's then DVD's...and finally on my hard drives.
As hard drives got cheaper and many companies offered large USB portable drives I copied all of my images from my hard drive on to these slow...but easy to use drives and took them off site. They were very portable but it generally took overnight to back up my over 200,000 current images. So what was next?
Then I purchased a removable single hard drive that ran at 7200 rpm's and it seemed to work fine. But again I had to do the back up and it took over 12 hours. Again...I would take this drive off site and replace it with another blank drive.
Recently, I discovered the RAID drive cost has come way down. This form of "duplication" has been around for years...but in the past it was very costly.
So about a month ago I purchased a StarTech Four bay RAID enclosure. The setup was simple and the device has worked fine since then.
It is a 4 bay enclosure. I purchased 3 drives for this unit. Two drives are installed at all times and set to RAID 1. As I bring images and data into the computer they are set to store on this external device. Everything is duplicated on the drives. So about every 10 days I remove one of the drives and put the 3rd drive in place. Immediately the device then duplicated whatever in on the drive that was left in the machine.
I take the removed device off site. The device runs until everything is duplicated on both devices....I have to do nothing.
The advantage of this unit is it works with Fire wire, USB 3.0 and before or eSATA.
The unit is about $225 and the drives were about $125 each. Your price may very based on the size of the drives you purchase.
Here are the product details for the one I purchased....by the way...there tech support people are really nice!
StarTech.com Four-Bay External SATA RAID Enclosure - Flexible Data Storage Solution
Designed for convenience, the enclosure features front panel LED indicators that provide RAID information and simple hard drive status and activity monitoring. The enclosure also features a built-in 3-speed 80mm fan with automatic or manual controls.