Does duplicati just not work with more than a few dozen GB?

I’m finding duplicati just plain doesn’t work well with datasets exceeding a few dozen gigabytes. OK, it technically works, but it takes literally days to create a base image for larger datasets.

By comparison, Macrium Reflect basically hits the limit of the transit medium (SATA, USB, Ethernet, whatever). It can easily hit gigabits per second with the right combination (eg.: nVME to nVME over USB-C).

Why is Duplicati so slow?

You can’t relay compare block level backup apps with something like Duplicati.
A fair comparison would be backup data with Macrium Reflect ( potenciály without compression) any then run dedupe on target data ( for example via build-in Windows deduplication Understanding Data Deduplication | Microsoft Learn ). And do that after every backup.

Duplicati will definitely be much faster:)

You’d think so, but Macrium File & Folder backup (not block level) is still substantially faster than duplicati.

I will concede that Duplicati is not the fastest backup solution if your measure is raw transfer speed.

I use Duplicati to back up virtual machine images that are in the 500 GB range, and the backups only take about 1-2 hours to run every night. True, the initial backup takes a little longer, but definitely not days on local network storage. The block level deduplication allows me to keep a 30 day rolling set of backups in a much smaller space than most other backup products I am familiar with.

In one instance I am able to keep 30 nightly backups of a 676 GB set of VMs in about 950 GB.

For me where Duplicati really shines is for offsite backups. In my area it is uncommon to have an upload speed faster than 5-10 Mbps. All the raw transfer speed in the world won’t help you when it’s bottlenecked through a slow network link. In cases like that I suspect that Duplicati would be just as fast as Macrium, or perhaps even faster depending on how many duplicate blocks there were.

I’m not familiar with Macrium products, but I suspect it’s not exactly an apples to apples comparison.