pve-zsync is still under development so there will probably be an official page when it gets close to being on the pve web gui. In the mean time anyone can add to the wiki.
I used pve-zsync for about a year. After switching our kvm storage from local to napp-it/iscsi we are now using znapzend on omnios . I've only used it a couple of weeks - it is working great so far.
"Will pve-zsync create snapshot if it will not reach other host/fail to replicate?" I am not sure. I did have an issue when i restarted the target in the middle of a send. a snapshot would need to get deleted . That happened a few times.
I've a question: what happens if you reboot a send or receive host during the middle of a zfs-auto-snapshot ? Does it auto recover?
"Should I keep only one snapshotter?" I think that is a good idea. So if I screw up the configuration on one, the other would hopefully still be working.
PS:
Check out znapzend.
http://www.znapzend.org/
https://github.com/oetiker/znapzend/blob/master/README.md
I like these:
"ZnapZend stores all its configuration in custom ZFS properties. So all configuration is hooked right into the ZFS fileset structure. When you modify the fileset, rename it, remove it, ZnapZend will happily chug along. ZnapZend comes with a special tool for setting and checking the backup configuration."
Have not tested, but it seems like ZnapZend will just work if the zfs is migrated to another system running ZnapZend. TBD
" You can configure any number of remote destinations for a fileset."
I think it is something that pve-zync could use since : "ZnapZend uses the built-in snapshot functionality of ZFS for fully consistent backups. For each fileset, a pre- and post-snapshot command can be configured"
So a command to send the Proxmox configuration file for the snapshot can be dealt with.