I use FreeFileSync. It's the only GUI tool I found that let's me sync folders while omitting file deletions. It lets you create batch files from the GUI that I execute with crontab multiple times per day.
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I am old school. I just use GNU Tar with the Pax format and multiple external detachable encypted hard drives. Reason is it is simple and a well known tool that is very common with a standard archive format.
I'm currently using TimeShift to backup my desktop onto an external hard drive (the why is because of how simple it is to use) and I'll be making a copy of anything I upload to my jellyfin server onto the external hard drive as well. I hope to eventually have a dedicated backup server and have a duplicate of it at a friend's house for offside backup too
I only have backups of my important files, encrypted and synced through rclone.
I've used Borg for years now. It's been rock solid. I test my backups regularly and have done several actual recoveries. I trust it with my data, which is the best thing I can say about backup software.
What is your strategie for testing? I am also using borg but i am not sure how to properly test it. Was thinking of a VM. But the data is way to much for it.
I work with VMs mostly, so I go for Veeam B&R. The free tier allows you to backup 10 VMs or machines.