Hi @zooney,
For (a), We’re still investigating but it seems that the error is coming from etcd/raft which is the package we use for raft consensus (raft/raft.go at d9907d6ac6baaebc3c9fd4e67acaa4154d2b3cd3 · etcd-io/raft · GitHub)
For (b), the w dir is for raft’s write ahead log (we use raft to replicate and agree on data in a multi-node setup). What it does is it persists raft entries/logs to disk every time a node receives a write (if it’s a leader) or a message to replicate from the leader (if it’s a follower).
So if you delete w and restart alpha, the data loss that you can expect are from writes that are not yet committed by zero and thus not written to disk yet. Because by that point it would’ve only been written in-memory and to the raft write ahead log. The in-memory data will be gone on restart since it’s not persisted yet while the raft write ahead log will be gone if you delete the w dir.