A Buffalo LinkStation that vanished from the office network without warning — no shares, nothing in This PC, and increasingly reluctant to power on at all. But it still answered a ping, which is a far more informative fact than it appears.
This is a scenario, not a case study. It describes a failure pattern we handle regularly and how it is approached, written from the technical work rather than from one client's job. Our documented case files are here.
The unit powers up, the lights look normal, and it answers a ping. The web interface may even load. But the shares are absent, or present and empty, and the unit reports no volume or an unmounted one.
Most NAS units keep their operating system on a small partition replicated across every member, separate from the data volume. That is why a unit with a completely broken data array still boots, still serves its web interface and still answers on the network — it is running from a partition that is fine.
So a responsive unit with no shares tells you something useful: the hardware works, the network works, and the problem is confined to the data volume. That is a considerably better starting position than a dead chassis.
It also means the unit's own diagnostics are running normally and will confidently offer to fix things.
A member dropped and the array is degraded past its tolerance. Two disks out of a RAID 5, or one out of a stripe. The disks are usually fine and the array simply will not assemble.
File system damage on an otherwise healthy array. The array assembles and the ext4 or Btrfs structure above it is corrupt, frequently after an unclean shutdown.
Metadata damage in a layer between the two. LVM, thin provisioning or the vendor's own volume manager. The array is healthy, the file system is intact, and the map connecting them is not.
Distinguishing the three is what the diagnostic does, and each has a different route back.