Question
A stateful service node backed by a network-attached block volume starts throwing I/O errors: the application logs `EIO` / read-only filesystem errors, writes fail, and the process is wedging. On-call sees: the node's other locally-attached disks are fine; the cloud console shows the network block volume briefly entered an 'error' / reattach state ~3 minutes ago (the hypervisor live-migrated or the volume had a transient backend blip), and after it recovered the OS still has the old device handle, so the filesystem got remounted read-only by the kernel after detecting write errors; `dmesg` shows 'I/O error, dev xvdf' and 'Remounting filesystem read-only'. The volume itself is intact in the backend; data isn't lost, but this node can't write. How do you triage a stale block-volume mount / transient detach?
Stop the bleeding first (mitigate), then form hypotheses from real signals. Separate root cause from symptom, communicate status as you go, and close with what prevents a repeat.