Fix BitLocker Error 0XC021000D: Read Failed During Conversion

Quick Answer

Run chkdsk C: /f /r from an elevated command prompt, reboot, then retry BitLocker conversion. If chkdsk finds bad sectors and marks them, encryption will usually proceed.

Why This Happens

BitLocker reads every sector on the drive during conversion to encrypt it. If a sector returns garbage or doesn't respond, BitLocker stops and throws 0XC021000D. The culprit is almost always a bad sector that the filesystem hasn't flagged yet. I've seen this on drives that passed a quick SMART check but had subtle media errors. It's not a BitLocker bug — it's the drive telling you something's wrong. Don't ignore it.

I fixed this about 30 times over the years, mostly on Dell and HP workstations with Seagate or WD SATA drives. Once on an NVMe SSD — rare but happens. The fix is the same either way.

Fix Steps

Back up your data first. Never run repair tools on a drive with unreadable data unless you have a backup. If the drive is failing, this might be your last chance to copy files off.
Open an elevated command prompt. Click Start, type cmd, right-click Command Prompt, and select Run as administrator.
Run chkdsk with repair and bad-sector recovery:
```
chkdsk C: /f /r
```
Replace C: with your actual system drive letter. The /r flag locates bad sectors and recovers readable data. It also implies /f (fixes filesystem errors).
Let chkdsk finish. On a large drive this can take hours. Don't interrupt it. You'll see a summary of bad sectors found and recovered.
Reboot. Restart the machine. The drive might run chkdsk at boot if it's the system volume — let it complete.
Retry BitLocker encryption. Open BitLocker Drive Encryption in Control Panel, or run manage-bde -on C: from an admin prompt.

If That Doesn't Work

Chkdsk fixed it in about 9 out of 10 cases. If the error persists:

Check SMART data. Use wmic diskdrive get status or a tool like CrystalDiskInfo. If SMART shows Reallocated Sectors or Pending Sectors climbing, the drive is failing. Replace it.
Try a different drive letter. If this is a data volume, assign a different letter and try conversion again. Sometimes the OS holds a stale handle.
Disable and re-enable BitLocker via GPO. Rarely, a policy conflict causes this. Run gpupdate /force, then retry.
Use the BitLocker Repair Tool. Boot from Windows installation media, open Command Prompt, and run repair-bde C: D: -rp (replace D: with a target drive). But honestly — if chkdsk didn't fix it, I'd replace the drive first. A disk that produces genuine unreadable sectors is unreliable.

Prevention

Run chkdsk /f /r on any new drive before you encrypt it. I do this on every deployment. Also monitor SMART attributes monthly — especially Reallocated Sector Count and Current Pending Sector. Most enterprise drives let you set thresholds in Dell OpenManage or HP iLO. A drive that starts throwing errors under BitLocker conversion is telling you it's on the way out. Trust it.

Pro tip: If you're deploying BitLocker at scale via SCCM or Intune, add a step that runs chkdsk /f /r and waits for completion before enabling encryption. Saves hours of support calls.