Losing a node is a regular occurrence, and a scenario for which Garage has been designed.
The assumption Garage makes, which is well-documented, is that of 3 replica nodes, only 1 will be in a crash-like situation at any time. With 1 crashed node, the cluster is still fully functional. With 2 crashed nodes, the cluster is unavailable until at least one additional node is recovered, but no data is lost.
In other words, Garage makes a very precise promise to its users, which is fully respected. Database corruption upon power loss enters in the definition of a "crash state", similarly to a node just being offline due to an internet connection loss. We recommend making metadata snapshots so that recovery of a crashed node is faster and simpler, but it's not required per se: Garage can always start over from an empty database and recover data from the remaining copies in the cluster.
To talk more about concrete scenarios: if you have 3 replicas in 3 different physical locations, the assumption of at-most one crashed node is pretty reasonable, it's quite unlikely that 2 of the 3 locations will be offline at the same time. Concerning data corruption on a power loss, the probability to lose power at 3 distant sites at the exact same time with the same data in the write buffers is extremely low, so I'd say in practice it's not a problem.
Of course, this all implies a Garage cluster running with 3-way replication, which everyone should do.
That is a much stronger guarantee than your documentation currently claims. One site falling over and being rebuilt without loss is great. One site losing power, corrupting the local state, then propagating that corruption to the rest of the cluster would not be fine. Different behaviours.
If I make certain assumptions and you respect them, I will give you certain guarantees. If you don't respect them, I won't guarantee anything. I won't guarantee that your data will be toast either.
If you can't guarantee anything for all the nodes losing power at the same time, that's really bad.
If it's just the write buffer at risk, that's fine. But the chance of overlapping power loss across multiple sites isn't low enough to risk all the existing data.
It sounds like that's a possibility, but why on earth would you take the time to setup a 3 node cluster of object storage for reliability and ignore one of the key tenants of what makes it reliable?
The assumption Garage makes, which is well-documented, is that of 3 replica nodes, only 1 will be in a crash-like situation at any time. With 1 crashed node, the cluster is still fully functional. With 2 crashed nodes, the cluster is unavailable until at least one additional node is recovered, but no data is lost.
In other words, Garage makes a very precise promise to its users, which is fully respected. Database corruption upon power loss enters in the definition of a "crash state", similarly to a node just being offline due to an internet connection loss. We recommend making metadata snapshots so that recovery of a crashed node is faster and simpler, but it's not required per se: Garage can always start over from an empty database and recover data from the remaining copies in the cluster.
To talk more about concrete scenarios: if you have 3 replicas in 3 different physical locations, the assumption of at-most one crashed node is pretty reasonable, it's quite unlikely that 2 of the 3 locations will be offline at the same time. Concerning data corruption on a power loss, the probability to lose power at 3 distant sites at the exact same time with the same data in the write buffers is extremely low, so I'd say in practice it's not a problem.
Of course, this all implies a Garage cluster running with 3-way replication, which everyone should do.