> But you cannot and should not rely on snapshots alone
That’s only for non atomic (multiple pools) snapshots. Isn’t?
Right. For single-filesystem installs it should be fine. Just make sure it has both the data and the WAL directories in the same one.
If I need to rely only on ZFS (automated) snapshots, then the best option would be to have two DB? Each one in each own pool. One HDD DB and one SSD DB. Then, the backend code should know on which DB the requested data is.
You could. I wouldn't -- I would set it up to use proper backups instead, maybe using snapshots as the infrastructure. That gives you other advantages as well, like being able to do PITR. It's a little more to set up, but I'd say it's worth it.