SDC / Whatever it is saying now / The disk is write-protected, or read-only

write-protected · read-only · lock switch · adapter · SanDisk KB 39716 · good blocks · permanent write protection · copy it now

The disk is write-protected, or read-only. A switch, an adapter, or the card deciding for you. The last one means tonight.

Windows says the disk is write-protected; a Mac says the disk is read only; a camera says the card is locked. Three different things produce it, and SanDisk's support note for the message lists them in order. On a full-size SD card there is a slider on the left edge, and a lever in the slot reads its position; slid down, the card is locked, and the slider gets knocked in bags and pockets. On a microSD in an adapter, the adapter's slider does the same job, and SanDisk's separate note on adapters says a loose switch may slide to the locked position as the card is placed in the host, and that the adapter should be replaced. The third cause is the card's own. SanDisk's note says that blocks can fail or go bad through usage and that the drive will write protect itself to prevent data loss when the number of good blocks is lower than the preset threshold, and a Linux kernel change of 2021 records that some SD cards set permanent write protection due to lifespan or internal problem. That lock is permanent, no utility clears it, and it is the card's last courtesy: it will still read, and everything should be copied off tonight. A card that reads is £149 + VAT after the free look, fixed in writing; a locked card that is also failing is £299 + VAT.

Free first lookOne fixed figure in writingNo data, no bill on most jobsReturn postage paid

Rather talk it through? An engineer answers the bench line
0800 6890668

Take the card out and leave it out. Do not format it, however politely the computer or the camera asks. Do not run chkdsk, First Aid, a repair tool or a recovery program that offers to fix the card. Do not keep trying it in reader after reader, and do not put it back in the camera to see. A card that reads a little tonight may not read at all tomorrow; whatever is on it is recovered from an image, and the image comes first.

Three causes, in the order SanDisk lists them.

The first is mechanical and belongs to full-size SD cards only. The slider on the card's edge does nothing inside the card; it is a notch that a lever in the slot feels, and the host decides from the lever's position whether to allow writes. A slider knocked down in a bag locks the card; a slider that has broken off, or a lever that has bent, locks every card or none. Slide it up, try a different slot, and if the message persists in a known-good reader with the switch up, the cause is elsewhere.

The second belongs to microSD cards in adapters. The adapter has a slider of its own, and SanDisk's note on locked microSD cards says that the switch may slide to the locked position as the card is placed in the host if the adapter lock switch is loose, and that the adapter should be replaced. A microSD card has no switch of its own; try it in a reader with a microSD slot, and if it writes there, the adapter is the fault and the card is fine.

The third belongs to the card. Flash wears out as it is written, and the controller keeps spare blocks to replace the ones that fail. SanDisk's note says the card keeps two copies of its own data on two different blocks and goes into write protection mode when corruption occurs on both, and that the drive will write protect itself to prevent data loss when the number of good blocks is lower than the preset threshold. Other makers' controllers do the same without saying so. The lock is in the controller's firmware, it is permanent, and it is set for a reason: the card can no longer promise to keep what it is given. It will still give back what it has, for a while. Copy everything off now, with a reader on a computer, and if the card reads too slowly or drops out, send it and let the bench image it in short passes with the power cycled between them.

The forum fixes are worth a paragraph because they cost time. diskpart's attributes disk clear readonly clears a flag Windows keeps about a disk; it does nothing to a lock the controller set. The registry key under StorageDevicePolicies does the same. The makers' format tools try to rebuild the card's table from scratch and, on a card that has locked itself, fail with Windows was unable to complete the format, which is its own page. None of them unlocks the card, and every attempt powers a card at the end of its life once more.

What it says, and what it means.

Describe yours to us →

What you see	The usual reason	Where that leaves you
Write-protected; SD card; switch up	The slot's lever, or the card's lock	Try another reader; if still locked, copy it off now
Write-protected; microSD in an adapter	The adapter's loose switch	Replace the adapter; the card is fine
Write-protected in every reader, switch up	End-of-life lock	Copy everything off; retire the card
Read-only, and reading slowly	Locked and failing	Imaged in short passes on the bench
Read-only after a dashcam or CCTV loop	Worn out, as the warranties warn	Everything inside the loop recovered

From the envelope arriving to your files going back.

Work we have closed →

Logged the day it lands, and the first look costs nothing Free

A case number goes on the envelope and a number on the card the day it is opened, with both sides photographed. The card goes into a reader on a hardware imager that controls how long each read may take, never a laptop slot, and what it presents is read first: its capacity, its identity registers, its file system. That decides whether it is a card a reader can see with a fault in the data, or a card whose controller has stopped, and which band it falls in. The first look is free, and you can stop there owing nothing.

Nothing to pay for lookingA single figure, put in writingNo formats, no repairs, nothing written

Imaged, sector by sector, before anything else

A card that answers at all is imaged in full on hardware that limits every read and retries on its own terms, weak areas last, with a map kept of what could not be read. A card that is slow, that drops out, or that has locked itself read-only is imaged the same way, in short passes with the power cycled between them. Nothing is written to the card at any stage, and every later step happens on the image.

Sector by sector, weak areas lastNothing written to the card

The flash read through the test pads when the controller has stopped

A card no reader sees is a monolith job. The coating is removed to expose the internal test pads, the pinout is matched against a database or mapped by hand, a needle adapter is fitted, and the raw flash is read out around the dead controller. The scrambling, the error-correction layout and the page and block order are then solved in software, and a virtual image of the card assembled from the raw dump.

Pinout, needles, raw dumpDescrambled and reassembled in software

The file system rebuilt, or the files carved, on the image

On the image, the FAT or exFAT tables are rebuilt where they are damaged and read where they are not, deleted entries are brought back, and where the tables are gone the photographs and video are carved out by their own signatures. Video files cut short by a dead battery are rebuilt from a reference clip from the same camera. Every photograph is opened before it goes on the list; a file that will not open is not counted.

Tables rebuilt, or files carvedEvery file opened before it is listed

You see the file list before you pay

What was recovered is listed for you first, and only then does a bill exist. Approve the list and it is invoiced; turn it down and it is not, and where nothing has come back, most jobs carry no charge at all. The files go home on fresh media with the card, tracked, with the postage paid here, and your case stays open until you have opened them yourself.

No charge until you accept the figureFresh media, supplied with the job3–5 days at the bench

From the bench

Try the card without the adapter before anything else. It is the commonest cause and the cheapest fix.
If the card locked itself, say how old it is and what it served in. A dashcam or a doorbell card locks after a few years of looping; it is the card being honest.
Copy off tonight if it reads at all. Tomorrow it may not.

1 in 3 cards that arrive here were formatted, repaired or rescanned by their owner first; nearly all of those would have been the lower band untouched.

One job, followed all the way through.

UK · SDC-2026-0716JOB LOGGED ✓

A Sony a6400's 64GB SanDisk Ultra card that went read-only in the camera and then on two computers with its switch up, carrying a month of a travel blogger's work she had meant to back up at the next hotel

The card had locked itself; its controller had run out of spare blocks. It read, slowly, and was imaged in short passes with the power cycled between them until every sector that would answer had answered. The exFAT volume mounted from the image and every frame and clip opened. The card went back with a note that it would never be writable again, and a suggestion for the next one.

100% of the month recovered3 days here, and back by post

Illustrative example — replace with a genuine case

What helps, and what harms.

Do this much first

Check the switch, and try without the adapter
Copy everything off at once if it reads
Say how old the card is and what it served in
Send it if it reads slowly or drops out

What sets us back

diskpart, the registry, or an unlock utility
The maker's format or repair tool
Putting it back in the camera to keep shooting
Leaving it for a week

Questions answered before you commit.

The card is write-protected and the switch is up. What now?

Try it without the adapter in a known-good reader. If it is still locked, the card has locked itself at the end of its life, which SanDisk's own note describes. Copy everything off now; it will not be writable again.

Can I unlock it with diskpart or a registry fix?

No. Those clear a flag the computer keeps, not a lock the card's controller set. They waste time the card does not have.

Why would a card lock itself?

Because its spare blocks have run out and it can no longer promise to keep what it is given. SanDisk says the card write-protects itself to prevent data loss. It is the card's last courtesy, and it still reads.

What does it cost?

If it reads, £149 + VAT after the free look; if it is locked and failing and must be imaged in passes, £299 + VAT. Fixed in writing, and on most jobs no data means no bill.

Where this usually leads.

Windows was unable to complete the format →Dashcam and security camera cards →SD, SDHC and SDXC →SanDisk →Card not recognised, or not showing up →

Nothing gets worse while the card is out of the device.

Looking at it is free. Back comes a list of what opened and what did not, together with a single price to finish, set down in writing while you are still free to say no. Until that list reaches you, leave the card in its bag and format nothing.

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Whatever it is saying now

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