20200426: UPDATE: Fixed the "pruned oldest snapshots" command.
A couple of years back I did a how-to about using a data backup utility called Duplicity to make offsite backups of Leandra to Backblaze B2. (referrer link) It worked just fine; it was stable, it was easy to script, you knew what it was doing. But over time it started to show its warts, as everything does. For starters, it was unusually slow when compared to the implementation of rsync Duplicity uses by itself. I spent some time digging into it and benchmarking as many functional modules as I could and it wasn't that. The bottleneck also didn't seem to be my network link, as much as I may complain about DSL from AT&T. Even after upgrading Leandra's network interface it didn't really fix the issue. Encryption before upload is a hard requirement for me but that didn't seem to be bogging backup runs down either upon investigation. I even thought it might have been the somewhat lesser read performance of RAID-5 on Leandra's storage array adding up, which is one of the reasons I started using RAID-1 when I upgraded her to btrfs. That didn't seem to make a difference, either.
Ultimately I decided that Duplicity was just too slow for my needs. Initial full backups aside (because uploading everything to offsite storage always sucks), it really shouldn't take three hours to do an incremental backup of at most 500 megabytes (out of over 30 terabytes). On top of that, Duplicity's ability to rotate out the oldest backups... just doesn't seem to work. I wasn't able to clean anything up automatically or manually. Even after making a brand-new full backup (which I try to do yearly regardless of how much time it takes) I wasn't able to coax Duplicity into rotating out the oldest increments and had to delete the B2 bucket manually (later, of course). So I did some asking around the Fediverse and listed my requirements. Somebody (I don't remember whom, sorry) turned me on to Restic because they use it on their servers in production. I did some research and decided to give it a try.