Don't use a synchronized folder as a backup solution (delete a file by mistake on your local replica -> the deletion gets replicated to the server -> you lose both copies).

old pc that has 2x 80gb, 120gb, 320gb, and 500gb hdd

You can make a JBOD array out of that using LVM (add all disks as PVs, create a single VG on top of that, create a single LV on top of that VG, create a filesystem on top of that LV, format it as ext4 filesystem, mount this filesystem somewhere, access it over SFTP or another file transfer protocol).

But if the disks are old, I wouldn't trust them as reliable backup storage. You can use them to store data that will be backed up somewhere else. Or as an expendable TEMP directory (this is what I do with my old disks).

My advice is get a large disk for this PC, store backups on that. You don't necessarily need RAID (RAID is a high availability mechanism, not a backup). Setup backup software on this old PC to pull automatic daily backups from your server (and possibly other devices/desktops... personally I don't bother with that. Anything that is not on the server is expendable). I use rsnapshot for that, simple config file, basic deduplication, simple filesystem-backed backups so I can access the files without any special software, gets the job done. There are a few threads here about backup software recommendations:

• What backup service do you use? - Lemmy.world
• What are your backup solutions? - Lemmy.world
• How do you guys back up your server? - Lemmy.world
• How do you backup things to your server? - Lemmy.world

In addition I make regular, manual, offsite copies of the backup server's backups/ directory to removable media (stash the drive somewhere where a disaster that destroys the backup server will not also destroy the offsite backup drive).

Prefer pull-based backup strategies, where hosts being backed up do not have write access to the backup server (else a compromised host could alter previous backups).

Monitor correct execution of backups (my simple solution to that, is to have cron create/update a state file after correct execution, and have the netdata agent check the date of last modification of this file. If it has not been modified in the last 24-25hrs, something is wrong and I get an alert).

I really love Kopia.

I mostly use it for cloud backups but it also works great for local/network storage as well.

It's really fast and efficient, supports cutting edge encryption and compression algorithms and the de-duplication and file-splitting features will let you generate frequent snapshots while costing you minimal storage.

Snapshots are also effortless to mount and it even supports error correction to protect against bit-flipping and other long-term storage risks.

It's also cross-platform and FOSS.

De-duplication prevents duplicate bits of data from being stored twice. Even if they are different file names or even synced from different systems.

The rolling hash/file-splitting means if you modify a 25GB file and only change a couple MB then only the changed couple MB will need to be stored. This means you can spend a month modifying small parts of a massive file thousands of times and avoid storing a new 25GB file thousands of times to archive those changes.

How old are these disks? If wouldn't trust anything of value to an HDD (better to save them on a bunch of good quality DVDs or BluRay disks than relying on such old disks.

Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:

4 acronyms in this thread; the most compressed thread commented on today has 8 acronyms.

[Thread #163 for this sub, first seen 24th Sep 2023, 18:15] [FAQ] [Full list] [Contact] [Source code]

Yes, storing each backup in 2+ places is best.

You can of course automate it. If you're running backups from Linux use anacron rather than cron because anacron tries to run when it can (when the machine turns on), whereas cron doesn't run again if the machine was off when it was time to run.

rsync is the most straightfoward solution. Pros: it won't copy files again if they haven't changed; it can copy remotely over ssh. Con: it has a bit of a learning curve.

BorgBackup would be my next recommendation, it takes distinct backups but doesn't duplicate files between them. It has compression, encryption (optional) and you can run checks on the backups. Con: for remote use you need to run a borg server on the target machine. Another potential con is that it doesn't store the files in a directly usable format like rsync. Borg archives are similar to a zip archive – you can list the files, you can extract them, you can even mount them somewhere and then access the files directly – but you can't access them directly without borg.

I'm sure there are more elegant solutions out there, but here's my method:

I have an inexpensive hard drive dock connected to my NUC home server via USB (with UASP support). I rotate two large-capacity hard drives between work and home, ensuring that one is always off-site. The drives are wholly encrypted, so I manually decrypt and mount the drive, and run a backup script that pulls any changed data from all devices on the network. I then take that drive to work and bring the other one home.

I have a calendar reminder to do this each month, and I'll sometimes run a backup in between the usual schedule when we're working on important projects at home.

How much data are we talking about? I get confused. Is it 1.5TB or is it 2.5TB?
Then, how backed up do you want to be? Think about if you REALLY need daily backups. While Raid might be cool and flashy; if you don't need it you don't need it and running it only creates cost.

If you have about 2 TB of data then i would just buy 3 external HDD of 2TB size and replace them every 5 Years. Then rotate them around every time you do a backup. Can you automate your backups? Not to the point of you not having to do anything. Unless you choose to pay for 2 cloud storage providers and both offer you to save your backups in an unchangeable state.

I personally don't use automation, I just have a Veracrypt volume for storing backups and do them manually. Rarely full-system, mostly just home folder.