I got asked several times how I do my backups and what strategy I would recommend. This will be a longer written answer for different needs. From the simple to the totally paranoid methods.
What are Backups and why should you care.
Backups are basically multiple copies of the same data in case the primary version gets damaged/destroyed.
If your primary storage fails and you don't have a second copy there is a huge chance that this data is lost.
There are ways to try to restore stuff, but that might fail based on the reason of the loss.
Here are some problems and strategies to prevent them in the order of protection and cost. They can be chained for extra security.
Protection against software issues or accidental deletion (user error)
The first layer is a simple copy of the files, you need into a different directory, maybe on the same physical medium. If your first primary version got destroyed, you have a copy.
Cost: basically none (storage space), protection level: minimal.
Protection against filesystem corruption
Problem: For whatever reason (power loss) or similar your computer can't read any data from that partition anymore.
Solution: To protect against that, create the copy on a different partition of the same storage medium. There are many tools that can repartition a drive to make space for a second partition.
Cost: basically none (storage space), protection level: better, but still minimal.
Protection against stroage medium breakage
Problem: The drive is no longer detected by the computer
Solution: copy the data to a different storage medium (another hard disk) to if the primary fails, you have a copy on another disk
Cost: 1 extra storage medium (can be cheap and slow), protection level: we get there slowly.
Side node: RAID
RAID or Redundant Array of Independent Disks is basically the one above in an automatic way. The drivers/operating system creates multiple copies of the files on it's own. This is the first step that
I would recommend for any serious work.
BUT a RAID is not a backup, it's just a convenient way for redundancy.
Protection against malware, "bad" software or severe computer damages or loss
Problem: A malicious software could delete or encrypt all copies on the computer, all storage medium could be destroyed by a faulty power supply or the computer/laptop gets stolen.
Solution: Like above, copy the data to a separate storage medium, but don't leave it attached. Use something like a USB-drive that you only plug in when reading or writing backups.
Cost: 1 extra storage medium in an USB case, protection level: good enough if you are not paranoid.
Backup Level beginner, recommendation 1
In a commercial environment I would suggest a RAID against storage medium loss plus backup on external USB attached drive. If one of the primary drives fail, you replace that and with a few minutes work you can continue work.
For private use a single medium with an addition external storage is a good and cheap solution.
But let's increase the problems and the paranoia level...
Protection against local disasters (fire, water, theft)
Problem: your backup drive sits on your desk and a local disaster destroys the computer and the backup drive
Solution: place your backup or better: another one in a remote area, at least on the other side of your flat/house. Ideally in a safe for elemtal (fire, water, wind) protection as well as theft.
Cost: 2 extra drives with 2 extra USB cases, protection: good for the non-paranoid
Protection against local disaster continued Part 2
To make you live easier, use a NAS (Network attached storage) to store your data via the network, without the need for plugging in a drive or two. If you place the NAS in the other part of your home you get better protection.
If the NAS uses a RAID, extra points for securing against drive failures. But this "always connected" opens up the malware part again where a software can destroy your copies. So this should not be your only backup strategy.
Using the "cloud" for backup
Similar to the NAS solution, you can upload your data into a cloud. But make sure the data is encrypted first and don't loose you enryption key.
And you need to trust your solution provider.
Protecting against bigger disaster
So you are afraid that a tornado can destroy your house and the local copy and the NAS? Add another backup to a remote location, similar to the cloud version for online version or simply place a hdd in a bank save in your bank.
Cost: higher, 1 extra medium with USB case plus banking fees, protection: very good
Storage medium issues
All above solutions have one thing in common: They use "normal" storage media. For long term storage (10+ years) they are not suited very well. Maybe simply because the hard disk from 10 years ago (like IDE, can't be connected anymore) or they fail. A used HDD that did not run for a few years has a chance to never spin up again because of mechanical failures. Burned CD/DVD drives become unreadable. Long term stability of SSD is not tested yet.
So lets roll back a few years and use a magnetic tape. What?
Magnetic tapes or LTO tapes are still around, quite cheap and very reliable
Modern LTO-8 generations can save up to 12 TB of data on a "cheap" 150€ tape (price: Mai 2020, price for external 12TB HDD ~270€). But the drives are very expensive 3500€+. But if you only need small amount of backup storage, use an old generation tape. LTO-3 with 400GB can be bought on auctions or IT-flea markets for less than 100€ and tapes for around 10€.
The software side: prevent overwrites on your backup medium
This is a software feature, not a hardware thing, but very important. Never overwrite your data on the backup. Always keep the old versions around. Some NAS or online backups support this directly. Here the software on the remote "thing" detects if the file exists, moves it out to a secure place and writes the new file. Sometimes this is called version control, historical files or similar. This protects from the scenario that your file got modified/damaged without you noticing and you overwrite your good copy with a bad copy. You can always go back to previous versions.
More software things: Make sure you reread and compare the data on the backup drive with the original to detect errors.
What would I recommend for the totally paranoid without budget limits?
On your main System, use a RAID 1 od RAID5, have one backup locally on another internal drive for quick "oops" moments. Have a daily backup to a USB-drive on your desk, a copy to a NAS with at least a RAID or a copy stored in a safe. Another copy in a remote location also synced daily. And a weekly copy on one tape for local storage in a local safe and one in your bank. If your local copies fail as well as the one in the safe and on the other side of the globe, there are issues where your backup is not that important anymore...
What software to use?
I can't give you any special recommendations, because your use case differs and I don't have any experience with commercial backup software.
Personally I use rsync to copy files around. It is a command line tool for (almost?) all up to date platforms. I use it on android, linux and windows.
For the very interested, here is my command:
rsync -abzO --partial-dir=.rsync-partial --force --ignore-errors --delete --backup-dir=/backup/archive/`date +%Y-%m-%d` rsync://firstname.lastname@example.org:/backup/snapshot source/dir
please refer to the rsync manual for the options and general how to use this very powerful tool.