The drive asks to be formatted, or shows up as RAW

What "RAW" means

RAW is not a file system. It is the word Windows uses in Disk Management when it looks at a volume and cannot identify what is on it. The volume exists, it has a size, it may even have a drive letter — but the structure at its front that would say "this is NTFS" or "this is exFAT" did not parse, so Windows declines to mount it and offers to format instead.

The important consequence: RAW is a statement about a few kilobytes at the start of the volume, not about the terabyte behind them. Your photographs are almost never involved in the failure that produced this message.

Why a healthy drive suddenly reads as RAW

Five causes, in rough order of how often they turn out to be the answer.

A damaged boot sector or file table

The volume's first sector holds the parameters everything else is calculated from. Corrupt it — by unplugging a drive mid-write, a power cut, or a card pulled out of a camera while it was saving — and the entire volume becomes unreadable to Windows even though every file on it is intact. NTFS keeps a backup of that sector in the last sector of the volume and a mirror of the start of its file table elsewhere, and recovery software can use those when the originals will not read.

A file system Windows does not know

Plug in a disk out of a NAS, a Linux machine, an Android device or a dual-boot computer and Windows will offer to format it — every time. The disk is fine and full of files; it is ext4, XFS or something else Windows has no reader for. Formatting here destroys a perfectly healthy volume. Unlost reads ext2, ext3, ext4 and XFS directly, and it can find volumes inside an LVM container, which is how disks from NAS boxes are usually arranged.

A BitLocker volume that has not been unlocked

An encrypted volume has no recognisable file system at its front, because the file system is inside the encryption. Sometimes Windows recognises this and asks for the password; sometimes — particularly for a BitLocker To Go drive on a machine that has never seen it — you get the format prompt instead. The data is intact and waiting for a key, and the key is very often in the owner's Microsoft account. Unlost recognises BitLocker and reports the recovery key's identifier rather than scanning for an hour and calling the drive dead.

A partition table that was damaged or partly rewritten

If the volume's start address is wrong, Windows reads the wrong place and finds nothing. The volume itself is untouched a little further along the disk. Searching the whole medium for the start of a file system finds it again.

Hardware that is failing

If the sectors holding the boot record cannot be read because the drive is dying, the symptom is the same message. This is the one case where speed of action matters and where scanning is the wrong first move — copy a failing drive before you scan it.

What not to do

• Do not format, however many times the dialog asks.
• Do not run chkdsk /f. On a genuinely RAW volume it will refuse anyway — "The type of the file system is RAW. CHKDSK is not available for RAW drives" — and on a volume it does accept, it rewrites the file system's own bookkeeping to make it self-consistent, which can mean discarding what points at your files. Repair after recovery, not before.
• Do not initialise the disk if Disk Management offers to. Initialising writes a new, empty partition table over the one that describes where your volumes are.
• Do not run a tool that offers to "convert RAW to NTFS". Anything that changes the file system writes to the drive. Get the files off first; the drive can be repaired or replaced afterwards.
• Do not keep replugging it. If the drive is failing, every power cycle is a risk with nothing gained.

How to get the files off

1. Leave the drive connected but unused, or unplug it until you are ready. Do not open it in Explorer and do not let any program point at it.
2. Install recovery software on a different drive — never on the RAW one, which Windows cannot write to anyway, and never on the drive you plan to recover to if space is tight.
3. Scan the volume read-only. Good software will not depend on Windows recognising the volume: it reads the disk itself, finds where volumes actually start, uses backup structures when the primary ones are damaged, and names what it finds — including "this is encrypted" or "this is XFS", which are answers rather than failures.
4. Recover to a healthy drive with enough room, then open a sample of the files.
5. Only then decide about the drive itself. If it is healthy hardware with a damaged file system, formatting it now is reasonable. If the drive caused the problem, replace it.

Questions about RAW drives

Will chkdsk fix a RAW drive?

No. CHKDSK does not run on RAW volumes at all, and where it does run it repairs the file system rather than rescuing files — sometimes by discarding the references that recovery would have used. Recover first.

Does RAW mean my drive is broken?

Usually not. Most RAW volumes are healthy media with a damaged structure at the front, a file system Windows cannot read, or encryption. The exception is a drive with read errors, which announces itself in other ways: clicking, stalling, disconnecting.

Why does Windows want to format my Linux or NAS disk?

Because it has no reader for ext4 or XFS and treats "I do not recognise this" as "this needs formatting". The disk is fine. Read it with software that understands those file systems and copy the files to a Windows drive.

Can I convert RAW back to NTFS without losing data?

Not reliably, and the attempt writes to the drive. The safe order is: recover the files to another drive, verify them, then format the drive if you still want to use it. Anything that promises an in-place repair of an unreadable volume is offering to gamble with the only copy you have.

The drive says 0 bytes, or shows the wrong capacity. Same thing?

Yes, usually the same cause. Those numbers come from the very structure that has been damaged. Reading the medium sector by sector ignores what the volume claims about itself.