Why is this better than rsync?
You cannot do this without help from the filesystem. That's why rsync itself does not support this, and it has to be done by a specialized btrfs tool in this case.
Getting into the unnecessary details: in classic live ISO fashion, the root (/) filesystem is tmpfs. Then I have at most 1 persistence drive and/or at most 1 9pfs mount. From there, I use bind mounts to only persist the few folders/files that I want preserved. For example, I'll have my persistence drive mounted at /persist and I'll bind mount "/var/lib/etcd" to "/persist/var/lib/etcd". Then when I reboot, everything outside of "/persist" is wiped out and I'm back to the initial iso + anything in /persist. So it is very similar to running a docker image with a volume mount, or running tails with persistence.
I build it all via NixOS and I use Impermanence to manage the bind mounts to the persist drive: https://wiki.nixos.org/wiki/Impermanence
That, and still claiming it’s “better than rsync”? Seems like you shouldn’t compare it with rsync (yet, if doing delta merges is planned)
- Single contributor. Software bugs are generally caused by developers writing code. By reducing the number of contributors, syq has cleverly reduced the surface area for defects to sneak in.
- Distribution via shell script. rsync is bundled in most linux distributions, which means you have to deal with annoying software updates from time to time. Syq, OTOH, tells you to pipe curl into bash to execute a shell script, which means one-and-done installation and maintenance.
- UI clarity. If you search StackOverflow for rsync, you'll see thousands of questions asking how to accomplish various tasks with rsync, both straightforward and arcane. By contrast, `syq` isn't even a tag on SO. The obvious conclusion here is that rsync's interface is so byzantine, and its documentation so poor, that users must resort to asking strangers for help, a problem obviously not shared by syq.
- You can install by piping curl to bash, using brew, or by compiling yourself. One thing about distribution I would argue syq gets right is that you are never relying on whatever version of syq happens to be installed on a server. The client syq always talks to a server syq tagged with the exact same version, and when your local copy of syq installs a remote copy, it verifies that the remote binary is signed by me.
- I never said or implied that rsync has a byzantine interface or poor documentation. I think rsync is well documented and the interface is overall fine. Syq even has an rsync compatibility mode, so you don't have to learn any new syntax if you don't want. Still, I tried to provide good docs for syq too, and honestly even if there were a gap in the docs, all you have to do these days is ask AI to look at the source code and tell you what to do. I think this also mitigates the trust issue with a new project from a single contributor.
Frankly, we would re-kick our fleet ahead of schedule rather then try to remediate it more manually. But we re-kick our fleet on a rotating yearly schedule, so it's not too much an effort to re-kick it earlier. It's a completely automated system in place now.