Data Error (Cyclic Redundancy Check): Causes and Fixes

You try to copy a file, open a folder, or initialize a drive and Windows stops with: “Data error (cyclic redundancy check).” It sounds cryptic, but it has a precise meaning — and knowing it tells you whether you’re facing a loose cable or a dying drive.

What the error actually means

A cyclic redundancy check (CRC) is a checksum. Every block of data on a drive is stored with a small mathematical fingerprint. When the data is read back, the fingerprint is recalculated. If the two don’t match, the data came back different from how it was written — and Windows refuses to hand you corrupted data, so it throws the CRC error.

In plain terms: the drive tried to read something and couldn’t read it correctly. The question is why.

The usual causes, from most to least benign

1. A bad cable, port, or USB enclosure. Data gets corrupted in transit, not on the disk. Very common with external drives and cheap cables.
2. A corrupted file system. An unsafe eject or power loss mid-write left the file system’s records inconsistent.
3. Bad sectors on the disk surface. The magnetic media (or, on flash, the memory cells) holding that data has degraded. This is the most common cause when the error keeps coming back on the same files.
4. A failing drive. Weak read heads or a dying controller produce errors across many files, often with slowdowns and freezes.

Step 1: Stop retrying the same copy

It’s tempting to hit “Try again” over and over. Don’t. If the cause is a bad sector, every retry makes the drive struggle to re-read a weak area, and on a mechanically failing drive that extra strain can cause further damage. Note which files fail and move on.

Step 2: Rule out the connection

• Swap the cable for a known-good one.
• Use a different port — directly on the computer, not a hub. On a desktop, try a rear port.
• Try the drive on another computer.

If the errors disappear, it was the connection.

Step 3: Check the drive’s health

Run CrystalDiskInfo or another SMART check and look at two things:

• UltraDMA CRC Error Count (C7 / 199) climbing → points to the cable or interface, not the disk. Replace the cable.
• Reallocated (05), Current Pending (C5 / 197), or Uncorrectable (C6 / 198) sectors above zero → the disk surface is degrading. Skip to Step 5.

Step 4: If the drive is healthy, repair the file system

If SMART is clean and the problem looks logical:

1. Open Command Prompt as administrator.
2. Run chkdsk X: /f (replace X with the drive letter). The /f switch fixes file-system errors.

Avoid chkdsk /r on a drive with important data you haven’t backed up. /r scans every sector of the disk and tries to relocate bad ones — on a weakening drive, that’s hours of stress that can push it over the edge, and it can “fix” files by truncating them.

Step 5: If the drive is degrading, copy first — carefully

When bad sectors are the cause, your goal is to get the data off before it gets worse:

• Copy your most important files first, smallest and most critical up front.
• Use a copy tool that skips unreadable files rather than stalling on them, then come back to the failures later.
• For a full rescue, professionals image the drive with tools that read the healthy areas first and return to the weak sectors last, minimizing stress.

When it’s time to stop

Power the drive down and get help if:

• The error appears on many different files, not just a few.
• The drive clicks, beeps, or slows to a crawl.
• It shows up when you try to initialize the disk in Disk Management (a sign the drive can’t read even its own partition table — see Disk Unknown, Not Initialized).
• SMART shows pending or uncorrectable sectors.

The bottom line

A CRC error means data couldn’t be read correctly. Check the cable first, then the drive’s SMART data. If the drive is healthy, chkdsk /f usually clears it. If SMART shows bad or pending sectors, stop repairing and start rescuing — copy what matters most, and don’t hammer the drive with full-surface scans.

If the files are irreplaceable and the drive is failing, our hard drive recovery service images degrading drives safely for one flat price — and you pay nothing unless we recover your data.