Morning Star Loc: West coast, North of the 49th N.

I have DropBox on desktop, laptop, tablet.... Space is limited, as I have the free version. But the space is more than sufficient to transfer files between devices and to send files to family and friends (and they do not have to have DropBox on their devices).
I have three 4TB external drives: One is my "working drive" (it's a physically smaller box, easier to have it sit beside the computer)- whatever images I work on go on there.
At the end of a working session, I copy all the images from the smaller drive to one of the "large boxes". When done, it is stored on the opposite end of the house from the computer.
Next time we go to visit our son and his family in a neighbouring town, the "large box" goes with me, to be swapped with the "large box" my 10-year old grandson is looking after for me. As soon as we're home again, that drive is brought up-to-date.
This way, I have three copies of each image (and when I leave them on the computer/in Dropbox as well, four). And the grandson is happy with a task he gets paid for: I occasionally give him $5.00 bill for "rent" of a corner on his bookshelf.

selmslie Loc: Fernandina Beach, FL, USA

For the last decade I have been using Allway Sync Pro ($26) on my desktop. It runs an incremental backup automatically for specific directories every three hours from 9 AM through 9 PM from my desktop to the two removable drives. I have the free version on my two laptops to run on demand.

Each month I swap one of the drives with the one in my safe deposit box and it catches up on the next cycle.

There are many other programs available. See Comparison of file synchronization software

tazman77 Loc: Wisconsin

Here is one that I found and used with success after lost all info on a 3TB external WD drive it cost me $39.99 and that was in decmber of 2017 have not had an issue since.
for windows : https://www.wondershare.net/ad/data-recovery/index-bing.html?utm_source=bing&utm_medium=ppc&utm_campaign=DataR&utm_term=wondershare%20data%20recovery%20reviews&utm_content=Brand%3A%20Wondershare

for a mac: https:https://0.r.bat.bing.com/?ld=d3lPjwmHmqDJDcy2TwoL39oDVUCUwacEsOwFweC-jubsjXsWmr9NrGE1Q8Nk6dRMemjpzITyWNFWTcL3EsQ3SqChnQTkfKnrcKYj4Q35fkMEpXMc5rAofnDfeyzhNUdEFlVFHUAhgjkK0zjrbNi1iasS8abQ1nVWPhxvKzfKaXmojNE8wx&u=download.wondershare.net%2fdata-recovery-mac_full830.dmg%3futm_source%3dbing%26utm_medium%3dcpc%26utm_campaign%3dDataR_SS_USA_pid(831)_%26utm_term%3ddata%2520%252Brecovery%2520%252Bwondershare%26utm_content%3dBrand%253A%2520Wondershare
check it out if you have data loss or delete something you should not have.

DJphoto Loc: SF Bay Area

I seriously considered Carbonite, but they are really just for backup and not file sharing. I share a lot of files with our kids and friends, so I went with DropBox. I have a TB and it works great. I believe DB and Carbonite are equally safe and reliable, it's just that DB fits my needs better. I checked recently, and I'm at 880GB, so I'll be increasing to 2TB in the near future. I also have everything on external drives and rotate one off-site at our daughter's house. I also have an internal drive where I keep an extra copy of all of my photos. I don't store my personal/financial data in the cloud, rather I want to keep "a closer rein" on it.