I have a special use case and don’t exactly if that works with Duplicati.
At home I use a normal PC, when not at home during the week I use a Laptop. I sync my important data via a cloud service or a USB stick so that when starting on every Computer I have the same data. Every evening I want to perform a backup. When working with my Laptop I want to do it from the source data there; when working with my PC I want to do it from the source data there. When I backup each with its own backup (from PC to external hard drive; from Laptop to a USB Stick) I in fact have all backup versions but distributed to two different backup destinations.
So my question: Is there a possibility to backup from two sources (with the same files, synced via the sync service) into on single backup destination? Or doesn’t that work because Duplicati would identify the files as totally different from each other? When I simply try to do this (with backup destination: USB stick) Duplicati says: Error while running [name of backup]. Database file does not exist: [Path]\Duplicati\KBTPXWWFDF.sqlite
Thanks a lot for some help with this!
Hello and welcome to the forum!
Short answer: No, each backup job on each PC must have a unique destination. The destination could be as simple a unique subfolder for each backup job in your target storage (B2 bucket, NAS share, etc). But you don’t want to mix two backup jobs together on the back end. It’s not allowed and you’ll end up messing up your backup data.
If this is something you really need, you could look at Duplicacy (name is similar but it’s a different backup program). It has something called lock-free deduplication and it DOES let you back up multiple computers/backup jobs to the exact same folder (global deduplication).
Thanks a lot. That is very helpful! 
I’m in a slightly different situation. I have an external drive that is accessed wirelessly by two different systems via NSA through my router. I would like to backup that external drive to the same folder in a cloud location regardless of which system is on line with the external drive at any given time.
Does this cause the same backup issues as noted above?
Thanks!
This presents a few challenges.
First, it can be difficult to back up remote files with Duplicati. It is really designed to back up files that are on local disks. That being said, some people have had success using Duplicati to back up files with mapped drive letters or UNC paths.
Second, Duplicati wouldn’t support being run on two different computers and backing up to the exact same destination. You’d need to configure the two computers to back up to different destinations. It could be as simple as a unique subfolder for each computer. This will not be very efficient and will potentially double the amount of space used. It’d probably be better to select one computer that is online the most to handle the backups.
Thanks for the quick answer.
I suspected this was going to be the answer, but wanted to ask anyway. I do mount the NAS as a local drive via fstab entry and use Duplicati to backup to pCloud (also mounted as a local drive).
So, best solution is pick the system that is most active and use that one to do the backup.
Thanks.