Disk storage for the WAL and periodic checkpoints can get you sub-second recovery targets easily.
Ninja edit: or a UPS and a shutdown procedure triggered by it that writes the database to disk. You can write 100GB in a couple minutes over a 10Gbps network. Faster to a local SSD.
Sub-second recovery and UPS triggered shutdowns are still nowhere near the reliability of a database ensuring fsync has been called when you call “commit”.
There are just certain classes of data (e.g. any kind of business transaction) where you can’t afford this type of best effort durability.
Ninja edit: or a UPS and a shutdown procedure triggered by it that writes the database to disk. You can write 100GB in a couple minutes over a 10Gbps network. Faster to a local SSD.