"What makes PlanetScale Metal performance so much better? With your storage and compute on the same server, you avoid the I/O network hops that traditional cloud databases require [...] Every PlanetScale database requires at least 2 replicas in addition to the primary. Semi-synchronous replication is always enabled. This ensures every write has reached stable storage in two availability zones before it’s acknowledged to the client."

Isn't there a contradiction between these two statements?

My personal experience with EBS analogs in China (Aliyun, Tencent, Huawei clouds) is that every disk will experience a fatal failure or a disconnection at least once a month, at any provisioned IOPS. I don't know what makes them so bad, but I gave up running any kinds of DB workloads on them, using node local storage instead. If there are durability constrains, I would spin up Longhorn or Rook on top of local storage. I can see replicas degrade from time to time, but overall systems work (nothing too large, maybe ~50K QPS).