When a drive, USB stick or memory card prompts you to format it before you can use it, it’s tempting to click yes — don’t. The prompt means Windows can see the device but can’t read its file system, and formatting would build a fresh, empty one over the top, discarding the index to your files. In most cases those files are still there. Here’s what the error means, why not to format, and how the data is recovered.
The device works — Windows just can’t read the file system on it, so it offers to make a new one. That new file system would sit on top of your files and the index to them. Formatting, or carrying on writing to the device, is what turns a recoverable problem into a lost one.
A storage device has two layers: your files, and a file system that indexes them so the computer knows where each one is. “You need to format the disk before you can use it’’ — and its relatives, “not accessible” and “the volume does not contain a recognised file system” — mean Windows can see the device but can no longer read that index. Its answer is to offer a format, which builds a brand-new, empty file system. That’s the trap: the new index goes on top of the old data, and once Windows is writing a fresh file system, the files it replaces get progressively harder to recover. The device isn’t asking to be wiped because it’s empty — it’s asking because it can’t read what’s there.
On USB sticks and SD cards, the usual cause is removal while the device was still being written to — pulling a card out of a camera or a stick out of a laptop mid-write leaves the file system half-written and unreadable. Flash wear is the other big one: cards and sticks have a limited number of write cycles, and as they wear, part of the file system can become unreadable and the whole device reads as RAW. On hard drives and external drives the same thing happens from power cuts, improper ejection, or bad sectors landing in the file-system tables — and on an external, a failing USB bridge can mimic it, so a different cable and port is always worth trying first.
Formatting doesn’t clean a device so much as lay a new, empty file system across it. On a hard drive, memory card or USB stick, a quick format mostly replaces the index, so data can often still be carved back afterwards — but it makes recovery harder and less complete, and any use of the device after formatting starts filling the space your old files occupy. On an SSD it’s worse: a format can trigger TRIM, which tells the drive to discard the old data for good. A memory card or USB stick has no TRIM, but a format still writes over the index you need. Whatever the device, recover the data before you format — not after.
The device is imaged read-only first, so nothing is written to it, and the file system is then rebuilt from that copy — or where it’s too damaged, the files are carved straight out of the raw data by their signatures. A memory card or USB stick is from £250 +VAT; a single hard drive is from £300 +VAT; an external drive is sent whole, since on a WD the encryption key lives on the bridge board and the bare disk is no use on its own. Every job starts with a free diagnostic and a fixed written quote.
No, not if you want the data. The prompt appears because Windows can see the drive but can’t read its file system, so it offers to build a fresh, empty one — which discards the index to your existing files. In most cases the files are still there. Recover them first; you can format afterwards if you still need to.
Almost always because it was removed while still being written to, which corrupts the file system, or because the flash is wearing out and part of the index has become unreadable. The card or stick often still holds the data. Stop using it and don’t format — continued writes are what overwrite recoverable files.
Usually, yes. The device is imaged read-only and the file system rebuilt from that copy, or the files carved out of the raw data directly. A memory card or USB stick is from £250 +VAT, a single drive from £300 +VAT, after a free diagnostic. The key is not to format or keep writing to it first.
A format writes a new, empty file system over the old one. On a hard drive, card or USB stick a quick format mostly replaces the index, so data can often still be carved back — but it makes recovery harder. On an SSD, formatting can trigger TRIM, which discards the old data for good. Either way, recover before you format.
Windows can detect the drive but can’t open its file system — often shown as ‘not accessible’ or a prompt to format. It’s usually corruption or bad sectors rather than total failure. On an external, try a different cable and port; if it persists, send the whole unit, since on a WD the key lives on the bridge board.
The files are usually still on the device under a corrupt file system. Before you click format or keep using it, send it in and we’ll image it read-only and rebuild the files from the copy — free diagnostic, fixed quote before any work.