Now, I've worked for more than ten years in IT, so I think I have a bit of insight of what's actually most likely to happen, and how a backup, and which backup, can save you from disaster. And what I'm about to write is just from my own perspective - that you're working with your photos on a single computer and are using a mainstream desktop operating system. I'm assuming that both the operating system and the data worthy of backing up are stored on one and the same computer, with a large enough internal hard disk.
I think that's actually a very desirable way of handling it, because, for the sake of convenience, if you can keep all the data together, from my point of view, you should. You might have an internal SSD as a fast boot device, and a large conventional hard disk for the data in your computer, or in other words, more than one single harddrive - that doesn't matter. I simply consider working with internal hard disks in a stand alone "client" type computer (desktop, workstation, laptop) preferable over using external hard drives for the permanent file storage. Drive letters and paths changing and whatnot are a pain in the brain. Internal hard disks keep things nice and easy.
Let's have a look at how disaster strikes first. In all these years that I've been working in IT, the by far most common scenarios where a backup was needed used to be:
- "help, I've accidentally deleted a file!" (and it's on a server share and not in the Windows recycle bin; pre Windows Server 2003 era, ie. no server side shadow copies)
- "help, my computer doesn't start anymore, it just makes a weird clicking sound all the time" (because the entire harddisk has failed)
But are cloud-based backups useful for #2? Not so. I have a simple question: how long does it take you to set up your computer, connect it to the internet, re-install all your applications, and then restore the data from a cloud-based backup? If you need to be back up and productive, the answer is: ages.
The most convenient way to keep the "downtime" short when disaster strikes in form of a total hard disk failure (reminder: it's the most common issue I saw on client computers) is a so-called "image" backup, and that's what I would like to recommend as a primary backup. A cloud-based backup for files is a convenience for the little bloopers like an accidentally deleted file, and I consider that a necessary, but albeit only secondary backup.
An "image" backup is a 1:1 copy of the computers hard disk(s) that is stored on another (most often external) hard disk. The software that creates these images either comes on a CD that can be booted, or it allows the creation of a so-called "rescue CD" that can be booted. Why? If your computers hard disk fails, there's no operating system to boot from of course. So if your hard disk fails you get a new hard disk, hook up the backup harddisk, boot the rescue CD, restore the image backup, and wait. For 400GB, the wait could be something like 5-6 hours. After that, you boot up your computer and are back on track. And that's the important part.
Do you think you can install your operating system, the drivers (for your screen calibrator), the software you need, etc. etc. etc. from scratch in 5-6 hours to then access your cloud-based backup? That's unlikely. And how long will it take to download all of your data from a cloud-based backup? Even if your internet connection is 50mbit or 100mbit downstream, downloading 400GB of data will take a veeeeery long time. It's just like that.
So, a local, image-based backup it is. For the sake of speed and convenience. So now about the how and when.
We're talking about photos, right? There is no way to get them back when the data is lost. Photos are not like your computers hardware that you buy again when it's toast. Photos are not programs that you can buy and/or download again. Photos are not digital downloads of music and videos that you can download again. Your photos are unique When you lose them and have to backup, they're gone. Forever!
With that in mind, it makes no sense at all to have one single backup of your computer's hard disk. Where do you store your backup hard disk? At home? Of course you do. What do you do if your home burns down, or burglarized, or flooded, or collapses because of an earthquake?
You need at least two sets of backups. Keep one at home for quick access. Store the other one in a drawer in your desk at work, or at the house of a trusted friend, that sort of thing. It's simple. It's convenient.