A lightning strike or a power surge does not destroy your data; it destroys the electronics that let you access it. On a hard drive, it is almost always the circuit board or the power supply that takes the hit, while the platters themselves remain intact. The result: in the vast majority of cases, replacing the burnt-out parts is enough to recover the content. Two reflexes matter first: do not keep stubbornly trying to power on a device that has suffered a surge, and be wary of any burnt smell.

What follows explains where the voltage spike comes from, what burns out depending on the device, and why the outlook often remains good.

Lightning, surge, wrong handling: where the spike comes from

Lightning and power surges come down to the same phenomenon: a sudden rise in voltage within an electrical current. This rise can have several origins.

The most mundane is mishandling, connecting something at the wrong voltage. Older SATA hard drives offer a good example. They used a Molex power connector supplying 12 volts and 5 volts. When that connector was slightly broken, or when it was forced, it was possible to plug it in the wrong way and send 12 volts where the drive expected only 5. The component does not survive that kind of mistake.

Next comes lightning proper, which causes a rise in voltage on the home's electrical network. If the computer's power supply does not have sufficient protection, the excess current forces its way through to the device and triggers a short circuit there. An important point: lightning does not need to strike your roof to reach you. It can hit a high-voltage line at a distance, and the surge then propagates through the network all the way to your outlets. This is why devices sometimes burn out several kilometres from the point of impact.

Finally, surges and short circuits are not the preserve of storms: they also accompany floods, when water connects points of a live circuit.

What burns out, and what can be saved

The good news lies in the way the current travels through the device: it first burns out what it encounters first, the electronics, before reaching, sometimes, what carries the data. The outlook therefore depends on the device.

Device	What often burns out	Recovery
Hard drive	Circuit board, sometimes the heads	Good: board swap and ROM transfer
SSD, USB stick	The controller, or secondary components	Variable: difficult if the controller is affected
Server, NAS	The upstream UPS, if present	Good: the server is often spared

On a hard drive, if the surge has stayed at the level of the circuit board, it is generally enough to replace that board and transfer the ROM onto it, the chip that contains the drive's own adaptation data, in order to recover the content. We have, however, already seen a case where the read/write heads had also been affected by the current: they then had to be replaced as well.

On an SSD or a USB stick, it is trickier. Sometimes it is secondary components, a capacitor, a resistor or a diode, that short-circuit and turn out to be defective: they can then be replaced. But very often, it is the controller that takes the surge, and you run into the full difficulty of recovering from an SSD with a dead controller, with the encryption and complexity that implies.

Burnt smell: the right moves

After a storm, it can happen that the fuses trip at home without there having been a surge in the internal network. A short circuit and a surge are not the same thing, and not everything burns out systematically.

One signal, however, does not lie: the burnt smell. If you notice it after a storm or an electrical incident, find its source before putting any device back into operation. And if that smell comes from a computer, do not try to switch it back on: take it straight to a specialist. Switching back on a device whose electronics have burnt out means risking making the damage worse and spreading the problem to components that are still healthy, right up to the storage device itself.

Let us clarify what we are talking about here. This is not a small, isolated short circuit caused by a defective component that keeps working after a fashion. We are talking about an entire board short-circuited by a surge. And even in that case, the chances of recovery generally remain very good, as long as the primary components, the memory chip or an SSD's controller, have not been affected.

Servers and NAS: the UPS takes the hit for you

For anything critical, a server or a NAS, the recommendation is clear: place it behind a UPS. The benefit goes beyond mere continuity of power in the event of an outage. In the event of a surge, it is almost always the UPS that takes the hit instead of the hardware. It sacrifices itself, goes out of service, and the server switches off without having suffered any direct damage. You then get an intact machine back, once the UPS has been replaced.

Conversely, a server or a NAS connected without a UPS or a surge protector finds itself exposed exactly like an ordinary computer, with the added risk of hitting several drives of a RAID at the same time. Upstream protection is therefore not a luxury: it is what decides, on the day of the storm, whether you lose a UPS or an entire server.

Prevention: UPS and surge protector

The rule is simple and varies according to the importance of the device. Anything critical, a server, a NAS, a workstation whose abrupt shutdown would cause damage, deserves a UPS, which protects against both outages and surges. Anything less critical but that stays permanently switched on benefits from being connected behind a surge protector, a power strip equipped with protection against surges.

And, as always, no electrical protection replaces a backup. A surge protector reduces the risk of hardware damage, but it is a copy of your data, elsewhere, that guarantees you will not lose anything on the day lightning gets through anyway.

Frequently asked questions

Does a lightning strike destroy the data on a hard drive?

Most often, no. The surge burns out the power supply and the circuit board of the drive, but the platters that carry the data generally remain intact. A board swap and the transfer of the ROM are then enough, in most cases, to recover the content.

Can a drive be recovered after a surge?

Yes, in most cases if only the circuit board is affected. It sometimes happens that the read/write heads are also affected and have to be replaced. On an SSD, the outlook depends on the state of the controller, which is harder to work around.

What should I do if I smell a burnt odour after a storm?

Find the source of the smell before switching anything back on. If it comes from a computer, do not put it back under power: take it to a specialist. Switching back on a device whose electronics have burnt out risks making the damage worse and reaching the storage device.

Does a UPS really protect my server from lightning?

For the most part, yes. In the event of a surge, it is the UPS that takes the hit and goes out of service, while the server switches off without direct damage. A server or a NAS without a UPS or a surge protector is exposed like any other computer.

Do I need a UPS or a surge protector?

For critical hardware (server, NAS), a UPS, which protects against outages and surges. For the rest, in particular whatever stays permanently switched on, at least a surge protector, a power strip with protection against surges. Neither of the two replaces a backup.

Can a surge affect several drives at once?

Yes. On an unprotected server or NAS, a surge can reach several drives of a RAID at the same time, and affect a whole fleet of workstations connected to the same electrical network. This is one of the reasons to protect critical hardware upstream.