Data Recovery Case File · NAS & Network Storage · The Appliance Boots From the Disks

NAS Not Discoverable After Being Powered Down

His enquiry was unusually well-informed and left little to establish. A mirrored two-bay NAS: "unable to connect to the NAS drive. It was powered down two weeks ago — on powering up yesterday, it is not discoverable. The disks on board can be easily removed, but I'm aware the partitions will not be FAT or similar. A quote for accessing and transferring the data would be appreciated." He already knows the two things most people do not: that the disks come out, and that their filesystem is not one Windows will read. So this page addresses what he has not yet been told — why a NAS that powers on can still be invisible, and why that symptom points at the disks rather than at his network. The answer is a detail about how these appliances are built that surprises almost everyone.

The decode: where the appliance's own system lives, and why the rest is fortunate

The detail nobody expects: a NAS looks like an appliance with firmware, in the way a router does. Most are not built that way. The unit's operating system lives on the member disks themselves — typically in a small system partition replicated across every disk in the unit, separate from the data volume. The appliance holds only enough in its own memory to start and hand over to that partition. Which means a disk problem can stop the whole unit booting: it powers, its fan spins, its lights come on, and it never gets far enough to bring up networking. So "not discoverable" is frequently a disk symptom rather than a network one, and hunting through routers, addresses and cables is the wrong search.

Why a fortnight's rest is the trigger: exactly as this archive has documented elsewhere. Disks in a NAS run continuously for years at a constant temperature. Powering down lets everything cool and come to rest, and the next spin-up is the most demanding moment a drive experiences — the motor overcoming static friction, bearings starting cold, heads unparking and calibrating. A disk quietly approaching the end of its margin can complete years of continuous service and then fail to survive its first restart. His shutdown did not cause this; it revealed a disk that had already reached its limit.

Why the configuration is fortunate: a mirror writes the same data to both members, so each disk holds a complete, independent copy. There is no layout to reconstruct, no stripe order to derive, and a weak region on one member can be answered from the other. Compared with the striped arrays elsewhere in this volume, where one damaged disk compromises every file, he could not have chosen better. It also means that even if the failing disk is the reason the unit will not boot, the data is very likely wholly present on the survivor.

The trap he has already half-anticipated: he knows the filesystem is not FAT, and the consequence is the important one. Connect one of these disks to a Windows machine and it will appear as an unformatted or unrecognised drive, and Windows will offer to initialise or format it. Accepting that on a mirror member destroys a complete copy of everything. Extraction has to happen from the Linux filesystem and be written to something his own computer can read — which is exactly the transfer he asked to be quoted for.

On the bench

Both members were imaged write-blocked on the Atola TaskForce 2 — both rather than one, because a mirror's advantage is only realised if the second copy is available to answer for any weak region on the first. The array was then assembled from the images offline, where no appliance could attempt a resync and no host could offer to initialise anything, and the Linux volume was mounted from the copies. The contents were extracted with their folder structure, filenames and dates preserved, written to a Windows-native filesystem on fresh media, and then opened and browsed on a Windows machine before delivery — because a claim that data is readable on a platform is one you test on that platform.

The outcome

Both mirror members imaged, the volume read from the copies and the contents delivered on media verified on his own platform. Free assessment, one fixed written figure including VAT; where a drive has to be opened, 50% of parts and labour is payable upfront with the balance only on success — otherwise no recovery, no fee. The decode, for anyone whose NAS has stopped appearing: these appliances usually boot from a system partition on the member disks rather than from internal firmware, so a failing disk can stop the unit starting altogether — which means "not discoverable" is often a disk symptom and not a network one; a fortnight powered down did not cause it, because spin-up from cold is the hardest thing a drive ever does and simply reveals one already at its limit; a mirror means each disk holds a complete copy, which is the best position available; and never let a computer initialise or format a member.

Our case files are drawn from genuine enquiries received by our laboratory over the past ten years, anonymised to protect client confidentiality. Each one describes the diagnostic and recovery procedure our engineers apply to that fault, using the equipment listed.