[this post has been copied from a reply to a question in Q&A about cloud storage for backing up your photos]
I can't remember who recommended them but I have ended up subscribing to Backblaze for my backups, since Time Machine is not compatible with my multiple external drives and there is also a bug in the software if you use 2 Thunderbolt displays (the system will not let you enter the restore screen unless you disconnect one of the screens).
The Backblaze solution costs $7 per month per computer and offers "unlimited" backup storage of the files located on that computer and its attached hard drives. I have 4 external drives (now including the original 6TB Time Machine drive) for a total of 15TB of external storage. Of that I am using about 6TB. Installing the software to your Mac is very simple and once done it creates a little icon in the menu bar. There is also a new section added to the Mac preferences specifically for Backblaze (which was created by former Apple engineers, so they know the macOS).
The backups run in the background so you don't really see what's going on and when I was going through the trial period I didn't notice any performance issues. You can set up preferences on how much of your bandwidth the system uses though, so that's helpful if you are on a slow connection. At the time of my first backup I was using a 20Mbps fibre line and my initial 4TB backup took about 4 weeks! When I moved house my fibre line improved and just a week ago I copied all the files that were on my 4TB main working drive to the 6TB drive because that 4TB has begun acting strangely. The addition of that 6TB drive to Backblaze containing around 2.5TB of data) only took 2 days to backup on a 50Mbps fibre line. That's not too bad.
This is what your online account looks like and at the bottom it shows you what drives you have backed up.
There is also an app for your phone that you can install and it will let you have access to anything on your backups which you can restore to your phone. That's a pretty neat feature.
However, here is the problem with this cloud solution;
If one of your drives remains disconnected from your computer for more than 30 days Backblaze will assume it is no longer required for backups and it will delete those files from the cloud. So if one of your drives fails and you need to get the files back you will need to restore that drive within those 30 days. If you have a slow connection or limited bandwidth this may be a problem for you, considering that my first backup took a whole month. Granted, that was 3 different drives for the initial backup, but if you are using very big drives on your computer you may need to upgrade your line speed.
Backblaze do offer to post you a replacement drive at the cost of $189 (max 8TB) and you can return the drive within 30 days for a refund, but obviously you would bear the costs of the mailing as well as import / export duty should you be outside of the USA.
Another option is to convert your backups into what they term B2 Cloud storage at the cost of $5 per TB. Basically this is like Amazon type storage where you pay to keep the files there in "buckets" and when you need to retrieve it you pay another cost. This could get quite expensive but I suppose in the event of a drive failure it would only be a temporary expense until such time as you can get the files back to your local machine. In my case with 6TB of data converted to B2 I'd be paying $7 for the backup subscription plus $30 for the B2 storage. Also, in B2 storage they don't keep your files in the folders you have them saved to on your local computer. You would have to create buckets for your collections and then somehow know what your file numbers are for any particular shoot you may have done. This would make it completely useless for me as my folder names are what I store my shoots in.
But for the $7 monthly fee for backups I think it is a worthwhile service that puts your mind at rest. You have offsite backups and you can get at them easily enough. US customers will have the drive mailing service to take advantage of, plus if you have a really fast internet connection you could probably download the files on any failed hard drive in a relatively short space of time. This is what I would likely do. I can upgrade my line speed to 1000Mbps temporarily if need be and that would cost less than trying to get a hard drive couriered to me from the USA.
If you'd like to try out the service you can use this link and they will give you an extra month free. I will also get a free month, so come along, sign up.