You plug in an external drive, or start a laptop with a second disk, and Windows greets you with: “You need to format the disk in drive E: before you can use it. Do you want to format it?” Underneath are two buttons, Format disk and Cancel. If the drive holds the only copy of your photos, accounts or work files, the most important thing you can do is click Cancel. This guide explains what the message actually means, why formatting or “repairing” the drive can make recovery harder, and what to do next.
What the error really means
Windows shows this message when it can see the drive but cannot make sense of the file system on it. It does not mean your files have gone. It means the structures that tell Windows where everything is stored (the partition table, the boot sector, the NTFS Master File Table or the exFAT/FAT allocation tables) are unreadable or damaged. In Disk Management the partition will often show as RAW, and in File Explorer the drive may report 0 bytes or ask to be formatted every time you open it.
Related messages that point to the same kind of problem include:
- “The volume does not contain a recognized file system.”
- “The file or directory is corrupted and unreadable.”
- “The parameter is incorrect” or “Location is not available” when opening the drive.
- CHKDSK reporting “The type of the file system is RAW. CHKDSK is not available for RAW drives.”
Common causes
The message is the same whatever the cause, but the causes are very different, and that matters for what you should do next.
- Unsafe removal or power loss. Pulling a USB drive out while Windows is writing, or a power cut during a write, can leave the file system half-updated.
- Bad sectors on a failing hard drive. If the drive cannot read the few sectors that hold the boot sector or the start of the MFT, Windows sees nothing it recognises, even though most of the data area may still be readable. This is very common on older external hard drives.
- A failing USB bridge or enclosure. Many external drives, including some WD My Passport and Elements models, have a USB-to-SATA circuit board that can fail or, on some models, handle hardware encryption. A fault here can make a healthy disk look blank or RAW.
- A drive from another system. A disk formatted on a Mac (APFS or HFS+), in a NAS, or as part of a RAID set will often trigger the same prompt because Windows cannot read that format. In this case there may be nothing wrong with the data at all.
- Encryption. A BitLocker or VeraCrypt volume that is not unlocked can look like RAW or unformatted space.
- Malware or accidental changes to the partition table, for example after using a partitioning tool.
What not to do
Most of the avoidable data loss we see with this error comes from well-meant attempts to make the message go away.
- Do not click Format. A quick format writes a new, empty file system over the old one. Data can sometimes still be recovered afterwards, but the new structures overwrite the very areas a recovery relies on. A full format in modern Windows writes zeros across the whole partition, which leaves nothing to recover.
- Do not run CHKDSK /f or /r, or “Scan and fix” when Windows offers it. CHKDSK is designed to make a file system consistent, not to save your files. On a damaged volume it can delete or orphan entries it cannot reconcile, and on a drive with bad sectors the /r option forces hours of reads across weak areas, which can push a failing drive over the edge.
- Do not initialise the disk if Disk Management asks. Initialising writes a new partition table.
- Do not keep plugging it in and out, or run several free recovery tools one after another. Each attempt adds wear if the drive is physically failing.
- Do not install recovery software onto the affected drive or save recovered files back onto it.
Safe checks you can do
A few checks do not write anything to the drive and can help you decide what kind of problem you have:
- Listen to the drive. Clicking, buzzing, beeping or repeated spin-up and spin-down point to a physical fault. Power it off and leave it off.
- Think about where it came from. If the disk was last used in a Mac, a NAS or a RAID enclosure, connect it back to that system rather than formatting it in Windows.
- Try a different USB cable and port, ideally a rear port on a desktop. If the drive is slow to appear or freezes Explorer, it is more likely to be failing than simply corrupted.
- Look in Disk Management (right-click Start, Disk Management) without changing anything. Note whether the disk shows the right capacity, a RAW partition, or “Unknown / Not initialised”. A wrong or tiny capacity usually means a hardware or firmware problem.
If the drive is quiet, responsive and shows its full capacity, the problem is probably logical. If it is a copy of data you also have elsewhere, read-only recovery software may be worth trying, provided it saves recovered files to a different disk. If the data is important and there is any sign of a physical fault, stop and get it assessed first.
How a recovery lab deals with a RAW drive
In our lab the first job is to make the drive safe to read. We check its physical health, then make a sector-by-sector image so that no further work is done on the original. Damaged file system structures are then rebuilt or worked around on the copy, and files are extracted from it. Where the cause is a failing USB bridge, we can often connect the disk directly; where it is hardware-encrypted by the enclosure, the original board may be needed, so please keep it with the drive.
You can read more about our hard drive data recovery service in London, our laptop data recovery, and how we handle data recovery for customers across the UK.
Get a free consultation
If Windows is asking you to format a drive that holds data you cannot replace, press Cancel, unplug it and call Data Doctor on 020 7394 2529 for a free initial consultation. You can also bring it to our clean room lab at Unit 1, The Willows, 80 Willow Walk, London SE1 5SY.