> Rebuilding a cluster from the last-known-good backup should not take that long
It's not even clear if that's the right thing to do as a service provider.
Let's say you host a database on some database service, and the entire host is lost. I don't think you want the service provider to restore automatically from the last backup because it makes assumptions about what data loss you're tolerant to. If it just works from the last backup, suddenly you're potentially missing a day of transactions that you thought were there that magically disappears as opposed to knowing they disappeared from a hard break.
Restoring from backup doesn't mean you actually have to use it - just prepare it in case you need it. Since this can take time, starting such a restore early would be an insurance policy, if needed. If there are snapshots to apply after the last-known-good backup, all the better.
> Rebuilding a cluster from the last-known-good backup should not take that long
It's not even clear if that's the right thing to do as a service provider.
Let's say you host a database on some database service, and the entire host is lost. I don't think you want the service provider to restore automatically from the last backup because it makes assumptions about what data loss you're tolerant to. If it just works from the last backup, suddenly you're potentially missing a day of transactions that you thought were there that magically disappears as opposed to knowing they disappeared from a hard break.