[isotopp]

> I think the article is saying that a web server (customers) should be stateless, because everything important should be in a database (data track) on another host. And that database probably has application level handling for duplicating writes to another disk or another host.

Correct.

> Hardware level redundancy like raid1 seems useful because it simplifies handling a common failure case when a single HDD or NVME fails on a database server

Nobody needs that if your database does replicate. Cassandra replicates data. MySQL in a replication setup replicates data. And so on. Individual nodes in such a setup are as expendable as individual disks in a RAID. More so, because you get not only protection against a disk failure, but depending on deployment strategy also against loss of a node, a Rack or a Rack Row. Or even loss of DC or AZ.