I just started using Duplicati for local backups to an external drive, but I’m interested in using it to back up to Azure blob storage as well. What’s the recommended way to do this?
I could always set up two otherwise-identical backups to store to the two different locations, but that sounds like it would be a lot of extra work for Duplicati (scanning files twice, deduplicating twice, compressing twice…). Is there a way to set up backups to multiple storage providers which avoids that?
One approach is to have two backup jobs. But what I do is just set up one backup job to target my local NAS, then the NAS will sync to cloud storage. Synology has a “Cloud Sync” package which makes this really easy. “rclone” is another nice tool that can sync local storage to myriad cloud providers.
Sadly, my NAS is too old and crusty (and cheap) to be able to sync to the cloud. 
rclone looks promising, though; I’ll check it out. Thanks!
Although it’s a bit more work (and somewhat duplicative) I would suggest sticking with two separate backup jobs. That way, if one of the jobs starts failing (disk crash, data corruption, Internet outage, whatever), you’ll still have a complete backup in at least one location. With the cloud sync/rsync method, if your NAS has difficulties or corruption you risk losing all your dependent backup sets.
Yes, it’s a bit more work for Duplicati, and perhaps it will take a bit more time to complete both, but you greatly increase the safety factor of your backup operations. Having had way too many backup locations fail for one reason or another, I’ll settle for redundancy over efficiency every time.
You might even consider to use two different tools for the local/remote backup.
e.g. rclone for local backup and duplicati for remote backup (from the same source)